Good cooler = Good HSF = Good Heatsink/Fan.
A poor cooler won't let you overclock much at all. A good one will let you get a fairly decent overclock. You don't even have to spend a lot of money for good coolers.
One of the best low cost heatsinks is the Spire/Speeze Falconrock II (about $12 USD). It comes with a weak fan which is really only good for stock speeds. However, add a decent, more powerful fan and it quickly becomes a good to excellent cooler (depending on how powerful a fan you add)[<-edit for clarity].
There are coolers that do a little better but they cost a lot more.
Going really cheap, some of the other Spire/Speeze heatsinks perform quite well (or so I hear). They are priced ridiculously low (about $8 USD) and you don't need to change the fans to do some decent overclocking. They are a bit noisy but they work well. I forget the models offhand but basically any of the models with a copper insert are a safe bet.
There are some Glacial Tech HSFs that work well (but some that are awful). I use the GlacialTech Igloo 2500 (not the PRO), not very loud yet OK for overclocking, good enough to run my Thunderbird C 1.0 at 1.5 Ghz and my Tbred B XP1700+ at 2.1 Ghz but definitely not what you would call an excellent HSF. It was a good compromise between cooling and noise.
I would have chosen a Falconrock II but I wasn't sure it would fit my motherboard. I later learned, too late, that it would.
Anyway, a good cooler should be for overclocking.
<b>56K, slow and steady does not win the race on internet!</b><P ID="edit"><FONT SIZE=-1><EM>Edited by phsstpok on 12/08/03 02:04 PM.</EM></FONT></P>