The Kalam cosmological argument, as it is commonly defended, is worded as follows:
1.) Whatever begins to exist has a cause.
2.) The Universe began to exist.
3.) Therefore, the Universe must have a cause.

To avoid the presupposition of an Aristotelian view of causality, we shall word it as follows:
1.) The Universe began to exist.
2.) Beginning to exist is a sufficient condition for requiring a causal explanation.
3.) Therefore, the Universe requires a causal explanation.

Let's begin. What evidence do we have in favor of premise (1), that the Universe began to exist? Let's start with the philosophical reasons that a past-eternal Universe is metaphysically impossible.

Firstly, a past-temporally infinite succession is logically impossible. The word "infinite" means literally "endless". So, given there were an infinite amount of past-time in the Universe, there would be a literal endless amount of past-temporal events within the history of the Universe. This means that it would require a literal endless amount of time to reach the present moment; if the amount of time it takes to reach the present moment never ends, then you never reach the present moment. You're only ever moving toward, but never actually reaching the present moment. Thus, metaphysically and logically speaking, a past-temporally infinite Universe is impossible. Given this, we don't need scientific evidence for a Universe with a beginning, since we've just discovered that it is logically impossible for the Universe to be temporally extended infinitely into the past. But, to humor myself and others, I shall provide the scientific evidence in favor the beginning of the Universe.

Let's start with the second law of thermodynamics, which states that, as time goes on, entropy (disorder) increases. On this theory, if the Universe has been here forever, then the Universe would have already run out of energy, thus, we would not be here. Well, we're here, so obviously the Universe has not been here forever. As Stephen Hawking puts it:

"But if your theory disagrees with the Second Law of Thermodynamics, it is in bad trouble. In fact, the theory that the universe has existed forever is in serious difficulty with the Second Law of Thermodynamics. The Second Law, states that disorder always increases with time. Like the argument about human progress, it indicates that there must have been a beginning. Otherwise, the universe would be in a state of complete disorder by now, and everything would be at the same temperature. In an infinite and everlasting universe, every line of sight would end on the surface of a star. This would mean that the night sky would have been as bright as the surface of the Sun. The only way of avoiding this problem would be if, for some reason, the stars did not shine before a certain time." (SOURCE: http://www.hawking.org.uk/the-beginning-of-time.html)

It is, then, obvious--at least by using the second law--that the Universe had a beginning. So, now we can move on to the second piece of scientific evidence that the Universe began to exist: the expansion of the Universe.

In the 1929, Edwin Hubble discovered (what is now known as Hubble's law) that galaxies are moving away from us, by detecting their redshift. As object move away from us, their wavelengths are stretched, caused the object to appear red. He noted that the further away the galaxy is, the redder they appear. This means that galaxies are moving away at a speed directly proportionate to their distance, which implies one thing: the space between the galaxies is expanding.

"In 1929, Edwin Hubble discovered that farther galaxies are going away from us at higher speeds, proportional to their distance. In other words, the spectra of more distant galaxies had higher redshifts. From distant galaxies, light takes millions or even billions of years to reach us. This means we are seeing an image from millions or billions of years ago. In redshift, the spectrum is shifted from shorter wavelength to longer wavelength as the light travels from the galaxy to us. This increase in wavelength is due to expansion of the very fabric of space itself over the years that the light was traveling. If the wavelength had doubled, space must have expanded by a factor of two. Thus, Hubble's discovery was that this expansion factor was roughly proportional to the distance light traveled, or equivalently, to how far back in time you looked. This means that the universe was smaller and smaller earlier and earlier. The universe has been expanding." (SOURCE: http://www.ugcs.caltech.edu/~yukimoon/BigBang/)

Given this, there must reach a point in the Universe's history at which the expansion stops and space terminates in a singularity, as per the Big Bang theory, as well as the Borde-Vilenkin-Guth theorem, from 2003 (which will be a forthcoming topic). If there is a place where the expansion of the Universe stops and space terminates, it must be a beginning to space(time) itself.

Moving on, the next piece of evidence to the beginning of the Universe is the cosmic microwave background (CMB) radiation, which is the radiation left over from the recombination of the Universe, which directly implies that the Universe began in a very hot and dense state, which is what would be expected given the Big Bang theory. Thus, given the CMBR, the Universe did begin in a "hot Big Bang" scenario as proposed and accepted by contemporary cosmology, implying that the Universe had a beginning.

Nextly, we shall examine the 2003 Borde-Vilenkin-Guth theorem which tells us--as its title directly states, and I quote--"inflationary spacetimes are not past-complete". In the BVG theorem, if we trace the relative velocities of projectiles into the past, at some point a finite time ago, they would have been at virtually the speed of light. This means that there is a physical boundary to spacetime, because physical mass/energy cannot travel faster than the speed of light. Thus, we cannot trace the histories of relative projectiles back any further beyond that boundary, known as the BVG boundary. In order to extend this boundary (and thus the hisotry of the Universe) indefinitely into the past, the upper limit velocity of physical mass/energy would have to be infinite, which implies that all particles would exist at every point of spacetime simultaneously; this means that all the physical matter in the Universe exists at every point of space all at once, which is blatantly not what we observe. Alexander Vilenkin has said that either this BVG boundary is the beginning of the Universe, or there is something before it, in which case it is the beginning of the Universe. Also, per the title once again, inflationary spacetimes are not past-complete, because the geodesics of inflation are incomplete into the past, requiring some new physics (if it exists) to describe moment before this boundary (if there even are any).

As we've now discovered, the evidence in favor of the beginning of the Universe vastly outweighs any evidence to the contrary, if not completely destroying it. Thus, the Big Bang theory can be assumed to be the beginning of the Universe, which directly implies that space and time physically came into existence at the Big Bang, and did not exist any any moments "prior", or rather, without.

"The big bang is not like an explosion of matter in otherwise empty space; rather, space itself began with the big bang and carried matter with it as it expanded. Physicists think that even time began with the big bang." (SOURCE: http://www.ugcs.caltech.edu/~yukimoon/BigBang/)

Now that we have established the soundness and validity of the first premise, we shall examine the second premise, that beginning to exist is a sufficient condition requiring a causal explanation.

If you name any object in existence, you can trace its history back to a moment where it no longer exists, thus meaning that if something does not exist, and then does, it must have a cause of this new-found existence. To assert causelessness is simply illusory, for if something has literally no cause of its existence, then by what means does it even come into existence? For anyone wishing to assert that causelessness can exist, they must answer the aforementioned question.
Typically, many skeptics have claimed that particle/anti-particle pair production (quantum fluctuation) happens without a cause, but it does not. The fluctuation of the vacuum energy is what causes the pair production. Thus, there is a cause to a quantum fluctuations. Secondly, this is to seriously misinterpret the merits and principles of not only science in general, but quantum mechanics. The law of causality is a properly basic and extremely fundamental property to science. Quantum mechanics does not operate causelessly, it operates indeterministically. Indeterministic causation is causation where one cannot determine (hence the term "indeterministic") precisely when the effect will be produced from its cause, but this does not negate there being a cause in the first place.

Thus, one can firmly contend with justification that the second premise is sound and valid.

If both of the premises are sound and valid, then it logically and inescapably follows that the conclusion--therefore, the Universe requires a causal explanation--is true.

At this point in the argument, we must deduce from all of the previous information what sorts of attributes the causal explanation of the Universe must have.
If the cause creates space, then it exists independently of space and so, sans the Universe, exists spacelessly, rendering it immaterial. If the cause creates time, then it exists independently of time at least sans the Universe, rendering it atemporal (timeless). Atemporality entails changelessness, because without time nothing can undergo real change. Thus, the cause of the Universe does not come into (or go out of) existence, as both are forms of real change. Thus--due to its atemporality--the cause must exist ceaselessly, or eternally.
If the cause of the Universe is eternal, then it must be personal. Impersonal causal agents cannot exist eternally without their effects also existing eternally. If the necessary and sufficient conditions which produce an effect are present literally forever, then any effects that they produce must be produced forever ago, and so the effect will also exist literally forever. An impersonal cause cannot do nothing forever, then produce its effect. Thus--given that the Universe is not eternal into the past, but its cause is by necessity--the cause must be personal, as to allow it to create a temporal effect from a timeless state. As I reiterate, if the cause were impersonal, then its effect would exist permanently and timelessly alongside its cause for an impersonal cause cannot do nothing forever, then produce its effect. However, a personal cause can. For instance, a man sitting down from eternity-past can freely will to stand up. But, the temperature being 212 degrees Fahrenheit (impersonal cause) forever means water will have been boiling forever.

Thus, we can conclude that the Universe has a cause, and that this cause is an immaterial, atemporal (at least sans creation), changeless (at least sans creation), eternal, and personal free agent-cause.
Therefore, the Kalam cosmological argument is both valid and sound, and is powerful evidence for the existence of a personal agent that, for all intents and purposes, is called "God".