The Sarong Theorem Archive, which claims to be "the only public repository of sarong-wearing mathematics images". If I had a sarong, and a digital camera with batteries in it, I'd be here. The people at the Secret Blogging Seminar have lamented the fact that this collection is not growing quickly. Incidentally, it seems to me that the best theorems for picture-taking are ones that have nice pictures associated with them, so I nominate Eric Paniagua proving the Pythagorean Theorem as the best of the lot.
Female mathematicians with teal hair. I'm not here because, well, my hair isn't teal. I don't know any of these people, although I went to college with a female mathematician named Teal.
On a more serious note, there are various pages which list a large number of mathematicians and have links to pictures of them; this is useful for putting a face to a name, although it would be more useful in the reverse direction of putting a name to a face. This is true in general; wouldn't it be nice to have something like identifont for faces? (Identifont asks a series of questions to help you identify an unknown font. After nineteen questions, it identified the font of this blog as Trebuchet, which is correct. I'm curious how exactly identifont works -- in particular, if I answer some questions wrong, can I still get the correct font? This is a question about error-correcting codes in disguise.) This isn't just for mathematicians, but for any population. There's a significant difference, though; usually when you're trying to identify a font, you have a sample of it in front of you, whereas if you have a picture of someone in front of you that would be good enough for such a method to be fruitful, you probably also know someone who knows their name. So a tree-like facial identifier patterned on Identifont would be more of a curiosity.