Apparently the top gaming CPU tom's hardware is recommending is the I5-750 (200 Bucks)
Nevertheless this article is an interesting read.
The new Core i5 brings top of the line Nehalem-class performance down to the $200 price point. We recently awarded it our Recommended Buy honor after seeing it stand up to more expensive CPUs in games and other demanding apps.
For those desiring the best possible performance, the Core i5-750 can be overclocked to great effect, performing similarly to the $1,000 Core i7-975 Extreme at its stock settings when pushed a bit.