Hey, Oly. Darwin's work and theories are the foundation of evolution by natural selection. Since his theory was correct, there won't be a competing theory to replace it, only work by others to build upon and refine it (i.e. advancing DNA/RNA methods, etc..).
It's for the same reason we do not have competing theories of what 2+2 equals; because the one we have is right. Do not think of Darwin's work as laws and theories, but as an interpretation of what Darwin observed and tested. His interpretation was largely correct, more so than he could imagine. We do have other interpretations, but they do not stand up to critical analysis.
As the great biologist J B S Haldane growled when asked what might disprove evolution: "Fossil rabbits in the pre-Cambrian..."
I think there could still be a few things that will rock the evolutionary world. We find small discoveries every year, like the recent finding that raptors probably had feathers. I am not informed enough about evolution to suggest some likely discoveries that are waiting out there to blow our minds, perhaps MP could suggests a few.
what leads you to believe that dude?
Because we are looking. Technology moves fast, we might be only a few decades away from finding it, if in fact life is common. There is some wishfull thinking too but I think that makes more sense than that life is rare, especially considering some of the scenarios by exobiologists. Advanced life I'm sure is pretty rare, at least in our immediate area. But how cool would it be to find life that can live in the methane seas on Titan or in the liquid water on Enceladus!
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Wouldnt biology as we know it remain consistent with observation? Aliens would still evolve in the same way we do, right?
Yes, but they might have a different genetic chemistry, even if subtly different from the essentially monolithic DNA chemistry every living thing from/on Earth has. Maybe a different palette of amino acids. That would indeed rock biochemnistry! cn
I think it's reasonable to say that aliens would evolve via natural selection, but there's no telling what environmental pressures they would endure so there's no way to determine how they would evolve.
I think a new type of replicating molecule different than DNA would be really incredible but a different set of nucleotides would also create a lot of questions and interesting investigations.
...in a symbolic sense (I know, I know...
) I like the 666 of the carbon atom. If I further that thought I see 777 as alien, 888 as christic, and 999 as all. I wonder what that would look like chemically. (einsteinium to the 9th?) ...no superscript for the apple nerds in the forum, that I know of 
Not "some new discovery"; I don't think that's the topic.