Most biology students are somewhat familiar with the concepts of homology and analogy in biology. Sandra Porter over at Discovering Biology in a Digital World has unearthed a really cool (no pun intended) example of analogous proteins-that is proteins that have the same function but differ wildly in structure. Check out her analysis of various anti freeze proteins.
This is an interesting analysis because often times intelligent design people treat proteins and protein design space as essentially one design for one function. Thus, if natural selection is some sort of search procedure then it is impossible time wise for natural selection to converge on a working protein related to a particular function. See for instance Dembski's paper on searching large design spaces. But what Sandra's analysis reminds us of is that protein design space isn't really all that sparse; radically different designs can have the same function.
In case you have forgotten what homology and analogy are all about:
A more technical look about phylogenetic reasoning and concepts of homology and analogy: