The universe had a beginning, and evidence that suggests this notion can be seen in the second law of thermodynamics, the expansion of the universe, radiation from the Big Bang, great galaxy seeds, and Einstein's theory of relativity.
The second law of thermodynamics says that the universe is running out of usable energy. One day the universe will simply run out of gas. If the universe had been running on its own energy from eternity, it would have been out of energy by now. But it has not, and so the universe must have begun in the distant (but not eternal) past. The universe, then, is not eternal but had a beginning.
In addition, in 1927, Edwin Hubble discovered that the light from distant galaxies was redder than it should be. Hubble concluded that it was redder because the universe was growing apart- in short, expanding! The light from the galaxies was changing because it was moving away from us. Furthermore, he found that the light was expanding in all directions, which means that it all came from a single point. There once was nothing, and then all of a sudden, there was something- the universe suddenly came into being in what is known today as the "Big Bang". There was no time, space, or matter before the Big Bang, but all came into existence at that moment.
In 1965, two Bell telephone Laboratory scientists discovered the radiation afterglow from the Big Bang. The light from the Big Bang is no longer visible, but the heat can still be detected. In 1948, scientists predicted that this radiation would exist if the Big Bang really did occur, and nearly twenty years later, it was discovered. This discovery confirmed that the universe is not eternal but had a beginning.
If the Big Bang had occurred, then scientists believed that we would see ripples in the temperature of the radiation discovered. In 1992, NASA's COBE satellite not only discovered the necessary ripples, but also found that the explosion and expansion of the universe were so precise that they allowed galaxy formation.
In 1916, Albert Einstein's calculations of his theory of general relativity revealed a definite beginning to all time, all matter, and all space.
In my response to "AtheistHeratic", I was trying to clarify that if the universe had a beginning then God would not need a cause, because only things that have a beginning need a cause.
Are you referring to the vacuum fluctuation models or the chaotic inflationary models when you refer to inflation and the universe in the same respect?