This site has become my main source for tour news. I don't go to many small-scale shows that you can't find on here since there's not a local scene that is conveniently close to me, so all the bigger tours that would interest me pretty much get covered here.
I do sometimes find out about tours on Facebook first too though.
2/7 Behemoth/Cannibal Corpse/AEON/Tribulation
5/21-24 Maryland Deathfest