How much are you willing to spend? The best air coolers are very good, the
Tuniq Tower 120 and the
Thermalright Ultra-120 Extreme are very good, but are around the $60 range. The Tuniq is probably slightly better depending on the fan you purchase for the Ultra-120. The Ultra-120 is $60~ without a fan, and then a good fan from say Scythe will run you around another $8 (120mm). Both are extremely quiet and perform very very good though. They are VERY large and employ a tun of heatpipes.
If you're not looking to spend that much Arctic Cooling offers the
Arctic Freezer 7 Pro for $35 at Newegg. This is the heatsink I use and is very good. Its very quiet and is basically a somewhat minture version of the popular tower heatsinks (like the two above). If you're not going to do any OCing I might just go with this, high quality, cheaper, and and will do the job fine.
You could do water cooling, but you need to spend $300~ to do it right and I would stay away from kits except for those from Zalman, Swiftech, and a few others, either way they're going to cost.