Right - on the computer my flatmate has just built:
Athlon XP 1800 (1.53 GHz)
Thermaltake Mini Super Orb heatsink (with two contra-rotating fans)
Attached by arctic silver 3
Lian-Li luminium case with 2 80mm intake fans and 3 outtakes (including a blowhole)
This runs at ~50 degrees with the system running at about 36-40 depending on ambient temperature. However, there has been a slight issue wth the heatsink. My flatmate originally planned to buy a 1.1 GHz Athlon and bought the Thermaltake to go with it. However, in the end he bought the XP 1800 on the cheap. But the thermaltake is only rated up to 1.5 GHz, so technically we're running it too hot, although we're well within performance tolerance. He's considering buying a better heatsink (such as the Thermaltake Volcano series), although they don't look as sexy as the Orbs.
If anyone wants to upgrade a heat sink, I'd suggest going for the Thermaltakes. Not only are they bloody god heat sinks, they're also really pretty. If you've got a window mod with lighting, you will want a thermaltake.
You know you want one