Variety just broke the news 10 minutes ago and I'm doing fist pumps and squealing like a small child with a brand new juice box.

From the article:

Paul Bettany, best known in the Marvel world for voicing Jarvis, Tony Stark's helpful A.I. system, will be playing the Vision in Marvel's "The Avengers: Age of Ultron."

Production starts next month, with director Joss Whedon and cast members like Robert Downey Jr. and Chris Evans. The Vision was an android created by the robotic villain Ultron, who was meant to be one of Ultron's henchmen but who instead turns against him and becomes a hero.

Absolutely love Paul in everything I have ever seen him in, and this is some excellent casting that anyone who is a fan of his, or the character, is sure to be excited about.