Wheels Mfg. makes replaceable derailleur hangers for most frames. Go to their website and sort by manufacturer to figure out which hanger you need. You can check out their website here:
http://wheelsmfg.com/content/section/4/27/
It can be bent back, but like others have said, hangers are made out of aluminum and fatigue. Bending it back may result in a crack, meaning you'll need a new hanger any way. The only way to bend it back precesily is with a hanger realignment tool. Most shops have these and will bend the hanger back, but will probably run you $20-25 for the service, since they'll probably do a derailleur adjustment as well.
I'd just go with a new hanger. They are really easy to replace - use a 5mm hex wrench to take off the derailleur, and then a smaller hex wrench (usually a 2.5 or 3mm) to take off the hanger.