Paul Bettany, the guy that voices JARVIS, will be playing the Vision. His costume (faintly teased in the above image) is said to be the classic red, green, and yellow version. Hopeful (but not expecting) that they'll reveal him in full tomorrow night at Marvel's SDCC presentation. They will most definitely be showing some kind of footage from Avengers there.
I'm also hopeful that they'll announce casting for Dr. Strange (fingers crossed for Benedict Cumberbatch) and announce the upcoming slate of unannounced movies (I've got hopes for Black Panther, the Inhumans, and a female-led movie, either Black Widow or Ms. Marvel; I'd also be pretty pumped if they split the Avengers 3 Infinity Gauntlet story into two).