If you purchased an Electronic Arts title on Steam, you'll be able to use it on EA's own Origin digital platform.
A little experimentation on Reddit—as well as investigation on my own—reveals that Origin will accept keys purchased on Steam, for the most part anyway. Origin appears to accept keys from Battlefield: Bad Company 2, Dragon Age: Origins, Dragon Age 2, Mass Effect 2 and Dead Space. Those are just the ones I've tried.
Unlike Steam, games downloaded from Origin do not require the Origin client to remain active in the background, so it's possible to run them on their own, or even with the Steam client if you prefer to stay in the loop with your friends list.
The Origin client currently auto-detects any EA titles installed on your hard drive, including ones installed on Steam.
Stay classy, EA.