You do need to give us the components that you have in the computer and what the case size is , also what do you have for a psu now? If you have a midtower and the standard ATX style form factor then a good 500w should work.
Review on the CM Extreme Power Plus 500W: http://www.hardwaresecrets.com/article/Cooler-Master-eX... Although it can actually deliver its rated wattage, it can't do so efficiently and goes out of ATX specs over 80% load. The EP+ series from CM is plaqued with a well-deserved reputation for having liar-labels and then costing too much for what you actually get.
Stay away from Diablotek! Diablotek is notorius for low-quality, high failure rate PSUs that take other components with them when they die. They're cheap for a reason.
If you're looking for a good, inexpensive PSU, then get the Corsair CX430: http://www.newegg.com/Product/Product.aspx?Item=N82E168... $35 after MIR. Those rebates are commonly $20 if you're willing to wait a few weeks for the next rebate. Without knowing what your system is it's hard to tell whether or not any recommendation is sufficient for your PC, but the CX430 shhould handle any PC with a graphics card up to an HD6850 level power draw.