Age of Empires 3 - I wouldn't worry about too much. It has never been a demanding game.
Arma 3 Alpha - According to user reviews, this game doesn't well support crossfire/sli yet.
Assassin's Creed 3 - Does not support crossfire well at the moment.
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BioShock Infinite - I'm getting between 50-60 fps most of the time (dips down into the 40s when there is LOTS to look at) (Note: You might need to update drivers to the most recent (non beta))
Borderlands 2 - Appears to work well with crossfire, mine is running well, but a few people are having issues
Chivalry: Medieval Warfare - I couldn't find anything recent to indicate it has fixed its crossfire problems from a half year ago (some people were running it fine with crossfire, some weren't)
Devil May Cry - It says it will support crossfire, I haven't found any proof or reviews/comments.
Diablo 3 - So long as you are in full screen it should run well
Dirt 3
Dishonored
Dota 2
The Elder Scrolls V: Skyrim
Far Cry 3
Guild Wars 2
Hawken
Hitman: Absolution
Just Cause 2
League of Legends
Mass Effect 3
NBA 2k13
Need for Speed: Most Wanted
Path of Exile
Saints Row: The Third
Sleeping Dogs
Sniper Elite V2
Tomb Raider 2013
Trials Evolution: Gold Edition
Worms: Revolution
XCOM: Enemy Unknown
Skyrim
Dota 2
League of Legends - Can Disable one card if it proves to be slightly buggy like mine (this is also not a demanding game)
I will update this post as I check out the games, gotta head off for a bit though.