I've got the Zalman 750 (yes a 750 should be plenty)(I just hate the blue LED's), and I'm using a 9850 (high wattage) it runs my system fine. Just get a good quality PSU, and it should last you through a few builds.
okay so i would suggest a good 600watt. im running a q6600 oc @ 3.0ghz and 2 gtx 260 in sli oc running on a 500w! just to be safe i would recommend 600w if ur gonna oc alot or if u add any extra hardrive, fans etc..
anything above 700w is just overkill.