If I were you I would go with the Great (Intel) one (i5 2400) + nVidia card (560ti) costs 754 in the sticky G?rm?n pointed out. Probably a bit less now. I just prefer intel over AMD, but AMD is a very viable option too, especially for gaming. Also I suggested nVidia over ATI, jsut coz I buy one card from ATI and than the next from nVidia, and now its vidias turn.
With the rest of the money I would get a decent monitor, I have a Samsung XL2370 and I am supper satisfied with it. It is a two year old model, so I am sure you can either get something better now for 250 usd or at least the xl2370 (I payed it a bit over 330 usd when I bought it).
If you already own a good monitor get a 64 gb ssd to speed up loading times or a nice sound card if you are in to music. Something in the lines of Asus xonar Essence ST or even ASUS Xonar DX (if you want to save a 100 bucks) if u like listening, or the M-AUDIO Audiophile 2496 (cheaper) or M-AUDIO Audiophile 192 (nothing more u need at home) if you are in to music recording and production.
Hope it helps