It seems nowadays that games or game trailers that utilize licensed music from lesser known artists do for those artists what many anime openings do for lesser known artists in Japan. Here are some licensed songs used in games/game trailers that either sold me on the song or the artist themselves.

Need for Speed Hot Pursuit - Opposite of Adults by Chiddy Bang
Street Fighter x Tekken - I Am In Love With You by Jared Evan and My Town by Hollywood Undead
Kingdom Hearts - Hikari/Simple and Clean by Utada Hikaru
Assassin's Creed Revelations - Iron by Woodkid
Burnout Revenge - Flyover by Asian Dub Foundation and The Great Escape by We the Scientists
Burnout Takedown - This Fire by Franz Ferdinand
Burnout Paradise - Rockstar (Jason Nevins Remix) by N.E.R.D and Going Through Changes by Army of Me
Jet Set Radio Future - Aisle 10 (Hello Alison) by Scapegoat Wax
Street Fighter III 3rd Strike Online Edition - Knock You Out by Adam Tensta
Mirror's Edge - Still Alive by Lisa Miskovsky

Plus there are probably a bunch from all the Madden and NBA games I've played but I can't think of any specifics.

Dead Space (http://www.youtube.com/watch?v=LAiHfqnbGYo) & the Prince of Persia remake (http://www.youtube.com/watch?v=DdZT6HIwoU4) helped me discover Sigur Ros.