I have a few favorites, with varying genres.
The Pillows: Feel-good Japanese rock, never fails to cheer me up on a bad day
Muse: Totally badass English band. Not sure what genre you could put them under, because they use a mix of guitar, piano, and even semi-orchestrated, electronic sounds. I'll just classify them under "fucking awesome" for now. They're one of the few bands I have the entire discography of.
Revocation, Allegaeon, and The Black Dahlia Murder: This one's a three-way tie, because out of all of today's death metal, these guys are the best of the best (at least in my opinion). It's a shame they aren't very well-known.
Daft Punk: You know these guys. Even if you don't think you do. You do.
Deadmau5: Yeah, yeah, he got mainstream. I don't care, he's still my favorite House (Hau5?) artist, and I love the guy's music to bits. He's a seriously nice guy in real life, too, so that's always a plus.