Some points:
I recommend the GTX560Ti as one of the best values.
Power Supplies:
1. the most important thing for a gamer is to ensure that the power supply supplies enough current on its 12V rail (or rails). There may be up to FOUR rails, but the total is not added. Never buy a PSU that does not tell you how much current (Amps) the 12V rail(s) supply.
2. 650W is typical for a high-end setup with no more than an HD5870 or 560Ti. Again, pay attention to the Amps for the 12V rail(s).
3. Quality is important.
Summary:
1. Get a GTX560Ti if in doubt, although there may be slightly better deals or even sales.
2. if a new PSU is required, look at places like NCIX, note the 12V Amperage (recommend at least 25% greater than the card you buy), spend time reading on PSU's in general and NEVER buy a PSU for which you have not found a good review.