Best brands out there are the Corsair, Seasonic, or PC Power % Cooling. Here is an example of an excellent buy and it is a 650 (which would allow you some room to upgrade in the near future), and it is the same price as a comparable 550. An excellent buy and about as good as it gets with a power supply:
http://www.newegg.com/Product/Produc...82E16817139005
Please understand, until you get a good power supply in there, we won't have any idea if this is the ONLY issue you have or if it will solve the issue. That is why I suggested you try to borrow one first. However, you do need a decent supply anyhow, so not much is lost if this is not the whole issue.