CPU - Get the K (2500K or 2700K) for an additional $15 because that is the one for overclocking. The straight 2500/2700 is locked at its top speed, no overclocking possible.

Also, I'd recommend a $30 coolermaster CPU cooler so you can run it harder.

As for video card, I'd recommend a GTX 580, but that's an additional $300.