I have a 2nd machine running a Sapphire HD 6870 and a i3-2120 and am using this modular PSU: http://www.newegg.com/Product/Product.aspx?Item=N82E16817182131
I build budget gamers for clients and have had excellent luck with Antec and Rosewill mid-range PSUs.
Use a PSU calculator to judge the size you need: http://www.thermaltake.outervision.com/
Idk what your budget is...but a good Corsair PSU does the trick. Also XFX and a few others make decent power supplies. Just make sure your power supply has the right amount of watts and enough on the 12v rail for all your components!