My tastes are quite predictable. A large base of popular modern rock music with some indie leanings and a smattering of post-rock, folk etc. I'd love to flesh out my library a bit more and get some more diverse music, but I don't really have the cash.
I can't rank my favourite bands, but the list would definitely have to include The Beatles, Radiohead, British Sea Power, Interpol, The Arcade Fire, Broken Social Scene, Bright Eyes, Neutral Milk Hotel, The Velvet Underground...gah, starting this list was a bad idea.
There's no way I can come close to picking a list of favourite songs. :p