My Diamond Monster used to get too hot to touch after a few hours of Quake, so I though I'd better do something about cooling.
This is my desktop case. Iv'e mounted 2 cpu fans, one above the other, on a slot blanking plate (with twist ties hehe). I then screw the mounting plate into the slot next to the card with the slot screw. This way the two fans blow air at the two processors on the 3D card.

I've positioned the fans so that they line up with the two card processors.
Yeah, I've run the card at a clock speed of 60 and it went fine but the gain wasn't that much to justify overclocking. I think performance is more hampered by my p166mmx cpu than the card.
Cost:
486 cpu fan from second hand computer shop: $5
Twist ties: $0
Blanking Plate $0
Total = $10
:)
Anyone else out their made their own cooling system?