PSU are good for people to install when they just start working on computers. It's takes a good, i don't know 20 minutes, helps get you used to doing stuff in there. I think you'd probably be pretty happy with the 7750, but you could step up to a 7770 too if you want to buy a new PSU. My 7770 will max out WoW.
Here's a good PSU to buy, this will handle a 7750, and a 7770, but not much more but that's why it doesn't cost so much. http://www.newegg.com/Product/Product.aspx?Item=N82E16817371045
People really like that VP series.