Was walking down King St yesterday. Went into the 'Hum' music store and heard the Mad World song. I'd heard it before vaguely but had no idea which artist had recorded it. Asked the guy behind the counter and he told me it was Gary Jules. You can get the song on the 'Donnie Darko' soundtrack or on Gary Jule's CD titled 'Trading Snakeoil for Wolf Tickets'. You can hear the 'Mad World' song at Gary's site at:
http://www.garyjules.com.