I'm glad you're asking, which indicates you realize the Logisys PSU-shaped object included with your case is not suitable for use as a computer power supply.
Anything built by Seasonic and at least 360W will be sufficient for that build; for upgrade potential, however, 500W would be more appropriate. In addition to their own, Seasonic builds PSUs for XFX, some Corsair (not the "Builder" units, which are CWT), and some Antec (VP is from FSP). FSP (their own, some Antec), Enermax/LEPA (their own), and Super Flower (new Kingwin and new Rosewill) are also good.
A few other suggestions: A 2x4GB RAM kit will offer better performance than 1x8GB since you will operate in dual-channel mode. A GTX550Ti is a relatively weak card for games. That one also appears to be a little overpriced; you can get the stronger HD7770 for less, and another $10-$20 will get the even more powerful GTX650Ti.
You may find a wired keyboard and mouse more consistent and reliable for games.
Edit: Personally, I prefer the WD Black drives, mostly for that longer warranty. Other drive warranties were reduced following the Thailand floods, which does not inspire confidence in whatever new materials and/or methods they may be using. I also suspect a brain fart, because the FX-8120 is Zambesi; the FX-8320 is the better Vishera (I do agree that that's the one you want).