I was looking for the Exodus thread so that I could post about seeing them live, but much to my surprise, they didn't have one. So here goes...
Exodus was a major player in the early Bay Area thrash scene and released their first demo in 1982 (featuring Kirk Hammett, before he moved to Metallica). While they've never had the virtuosity of Megadeth, the mainstream success of Metallica, or the extreme imagery of Slayer, Exodus has their own fun and aggressive brand of thrash... always with a sense of humour and never taking themselves too seriously. Their 1985 album,
Bonded by Blood, is an absolute classic of the genre and Paul Baloff's insane deranged vocal style there is the best in the business.
Since then, they've been through numerous lineup changes, a hiatus and deaths of band members, but they've still managed to release some good material today.
Tempo of the Damned from 2004 ranks among their best.
A Lesson in Violence from BBB
The Toxic Waltz from their follow-up album.
Everybody's doing the toxic waltz... Kick your friend in the head and have a ball 
Deathamphetamine from 2005