Who Is Elmo Blatch if you want "emo that doesn't suck".
Lately I've been really digging the virtual melodic heavy metal band Deathmole, you can find a pretty good selection of "their" stuff on last.fm.
Radiohead just makes me peach. From The Bends through In Rainbows, there is a Radiohead album to fit almost every mood.
http://www.thesixtyone.com has been a good source for a lot of the indy bands I have enjoyed lately, with a smattering of off-the-trail but popular stuff.
Iron and Wine is usually nice. Neko Chase. Obadiah Parker. JoCo (Jonathan Coulton) if you are feeling a bit geeky.
My First Earthquake if you want some eurotrash, Casio keyboard goodness.
Their selection of anti-folk is worth perusing.
They also have an intriguing selection of R&B/hiphop, not gangsta-gangbanger stuff, but some really intelligent, mellow and accessible stuff, for example check out Philadelphia Slick. Or if you enjoy the dj mix variety, they have a few tracks from Girltalk (but admittedly not their best material). Also check out DJ Catalyst, BEARBOT, and ugress.