I have a dual core and am considering an upgrade to an 8800. according to PC Gamer, (which I've subscribed to for many years), the 8800GTS offers 'superb value, giving top notch performance on all but the largest screens for half the price of its big brother' (£150-180). Tempting.
Crysis looks superb. I've now finished HL2 Ep2 and am looking for something new and exciting!