For a extreme quad core with extreme overclocking, you should go with water. But if you insist on air, then Xigmatek S1283/Kingwin Revolution something (clone of Xigmatek), OCZ Vendetta 2 if you can find it or Tuniq and Termalright Ultra are best. The first 3 should be cheaper than the latter 2 and they also come with their own fans. There's also a Xigmatek RS1283 that comes with a very quiet fan if noise is an issue. For 9800gx2, your only aftermarket solution would be water. For the 8800GT, the Arctic Cooling Accelero S1 Rev2 is a great cooler that doesn't cost a lot but it doesn't come with a fan for active cooling. If you want a fan for the Accelero, any 92mm or 120mm fan will do. Otherwise, the Zalman VF1000 is a great cooler as well and comes with a fan.