For those looking for some solid examples of homebrew alien construction, I offer up The Warp's 10-part series of new aliens, which recently concluded with this entry. Be sure to look at the notation for year introduced and the various comments sections, as they give an indication of the general idea and timeline for each alien.
(Sidebar: I considered posting the link to the relevant Fantasy Flight Games page, which has the same information contained in one thread. In theory, this would be easier, right? Everything would be in one place. Here's an indication, though, of how brutally unreadable and user-unfriendly the FFG forums are: I don't want to subject anyone to having to read all of that white-on-gray text, and I don't want to be responsible for the interface-induced frustration that would be felt by anyone attempting to actually respond to the post. Sorry, FFG fans, but those forums are just plain awful.)
Okay, be that as it may, let's focus on the good stuff. Once again, here's 100 new aliens to play with, including quite a few that are intended for use with the new FFG edition. Go crazy, yo.