Water 
Recently I read in one of my feeds that IBM has found a way to cool their hardware with water ... actually built in a cabinet with watervents et al. Also, sometime back I had seen on some Discovery, or some other channel where some geeks had actually managed to pull this off with water being pumped into plastic tubes and plastic bags to cool off the cabinet.
Gel
Back when the AMD processors were notorious for heat generation, the firm had agreed to ship this heat absorbing gel to all users of AMD Athlon. You can try to get your hands on one of those gels.
Multiple Fans
If your cabinet is big enough, then you can setup multiple fans to drive out the hot air and bring in cooler air. It would make sense to take some time out and study the exact wind flow through your cabinet. Placing the multiple fans so that the wind flow goes over your GPU and Processor will help reduce the heat.
If all else fails, keep the cabinet open
Hope this helps!!