It has been confirmed that Attack on Titan will be airing on Adult Swim's Toonami starting May 3rd. This is about a month before eps 1-13 come out in a boxset.
It looks like it will be on early as well:
11:30 p.m. Attack on Titan
12:30 p.m. Space Dandy
1:30 a.m. One Piece
2:30 a.m. Black Lagoon
4:00 a.m. Fullmetal Alchemist: Brotherhood
I've seen this posted multiple places and got word of it via tumblr. For the Toonami trailer (and as a resource for the scheduling table) please click this link www.animenewsne....
For the several English dub trailers click this link www.funimation....
(Click videos under the AoT banner and there should be 5 trailers to view)
You can also pre-order either of the collectors edition of the first boxset from Funimation.com. They come with varying amounts of goodies. You can get a preview of them by clicking the link above and scrolling down.
I'm really not too surprised by this. I knew Toonami would pick it up. AoT is already crazy popular in the US. I can only imagine the boost in popularity it will get after airing on Toonami.