There are plenty of websites now that use your likes to suggest new things you might like, but the simplicity of TasteKid and the fact that I don't have to register and fill in a ton of my likes has won me over. In some cases, it's freakishly smart. I put one of my favorite bands into the search bar and the TasteKid told me some bands I might like, which were approximately 30 artists from my iTunes library, even some of the more obscure ones. Well played, TasteKid.
Also, no matter the kind of media you put in the search bar, band, book, or movie — it'll suggest all those types based on one thing you like; so say if you enter The Decemberists into the bar, they'll give you other bands, plus movies and books that are somehow related to that genre. It's like they know me.