LensHero
Since I'm one of those gear-junkie type photographers, I spend a lot of time researching camera bodies and lenses. My obsession has even helped a friend or two pick a lens (and get a good deal). My go-to resource has always been The Digital Picture; Bryan has ridiculously in-depth reviews, sample photos, and recommendations.
Today, though, I added another resource to the list: LensHero. They've got a nice little tool that lets you choose what kind of lens you're looking for and how much is in your budget. They also include a good deal of third party lenses, which I haven't spent a lot of time studying.
If you don't want to wade through a novel of information on each lens (I usually do), head on over there now and check it out.