Putting my pedant's hat on temporarily, I think people here are accepting the shorthand "evolution" meaning "the origin of species through evolution by natural selection", for which "the Darwinian theory" is a useful shorthand.

"Evolution" itself is a process, not a theory, as is "natural selection".

That natural selection will lead to evolution (in the short term) is one (lab-testable) theory, which even "creation scientists" will say they don't doubt. Once you acknowledge the role of genes in biology (itself "only" a theory, but a very solidly based one), it becomes very difficult to deny. The origin of species (in the long term) through evolution by natural selection is the full-blown Darwinian theory.

That said, one has to be clear about what are the alternative hypotheses which the Darwinian theory has successfully excluded. The main one that it excluded historically was the origin of species by Lamarckian evolution. http://en.wikipedia.org/wiki/Lamarckism (Contrariwise, Lamarckian evolution does seem to be a fairly good description of the evolution of knowledge itself.) People sometimes say that the Darwinian model is under threat from "punctuated equilibrium", but the reality is that such is within the scope of the Darwinian model, and these are just details of the practical operation. That (unsubstantiated and probably false) idea that the Darwinian process must be slow is not a necessity of the Darwinian theory, though because Darwin himself wrote it, many people suppose it is. I am not really aware of any other serious theory that has been proposed as an alternative to Darwinism, waiting to take over when the inconvenient evidence is unearthed. I suppose if some such substantially inconvenient scientific evidence should be unearthed, it will be back to the drawing board (compare "dark energy", being code for "something wrong with our present theories of the fundamental forces of nature"). Many people hypothesise the origin of species by magic (a general description, usually not adopted by those who propose specific versions of it), and suggest Darwinism should be capable of excluding it. But magic is not a testable theory, so no scientific theory is ever capable of excluding it; but by the same token there is no scientific mileage in it.