I recently found my old copy of A Brief History of Time (Stephen Hawking's book on cosmology & physics, aimed at the layman) and decided to give it a re-read. Early on, there is some interesting discussion of scientific theories.
His points are relevant to the whole creationism debate, since the one of the most frequent arguments made by creationists is that "evolution is just a theory" (with the implication being that a theory is no more than a guess). A scientific theory is quite a bit different from a guess - in fact, many consider theory to the highest product of the practice of science:
"A theory is a good theory if it satisfies two requirements: It must accurately describe a large class of observations on the basis of a model that contains only a few arbitrary elements, and it must make definite predictions about the results of future observations.
...
As philosopher of science Karl Popper has emphasized, a good theory is characterized by the fact that it makes a number of predictions that could in principle be disproved or falsified by observation. Each time new experiments are observed to agree with the predictions the theory survies, and our confidence in it is increased; but if ever a new observation is found to disagree, we have to abandon or modify the theory."
That, in a nutshell, describes why the theory of evolution is still accepted by the majority of the scientific community: because it has met the standards of a good, robust theory. Not because of any tinfoil hat, black helicopter-esque conspiracies amongst scientists.