Well you answered your own question, case off, fan in, no problem. I use to use those slot fans but gave up, not worth it in my mind, they just take away any space between your card and air flow. I went thru 2 or 3 of them and said the heck with em.
Sorry I really don't know of anyone selling a good heatsink/fan combo for ati cards. I looked at tennmax, no go.
I really think the best thing out is the twin turbo bay fans if you have an open 5 1/4 bay. Really move alot of air out of the case allowing cool air to come in.
If the ati card fan/heatsink is removalable sometimes it will help alot to redo the thermal paste they used if any. Artic silver is the best, but it is conductive, be very carefull not to get messy with it.
I'm running a mid tower antec case with two 80mm fans, a bay fan, stock gforce fan. P3 850 at 1054 runs at 35 c. Gets warmer playing quake3 or serious sam but doesn't get too warm.
Then again it maybe the chipset getting too warm, not the vid card at all.
Add some additional case fans, maybe a bay fan, look at the way the heatsink is attached to the vid card
Larger case is better for airflow, less mass in the way of the air.
Hope this answers part of your question.
couple places to shop around
http://www.3dcool.com/ http://www.2cooltek.com/ http://www.heatsinkfactory.com/
[Edited by brianF on 06-04-2001 at 10:19 PM]