...well, I've got the Thermalright SLK-900 on a P4 3.06G. 29C idle, 37C full load. I have a 92 mm Enermax adjustable fan on it. It's quiet and it cools better than anything else on the market using air at the moment. The advantage of the 900 over the 800 is that you can smack a 92 mm fan on it which cools the whole CPU neighborhood as well.
You didn't say whether you want to cool AMD or Intel, which is often two different routes...