with one of my old cases, I did a really wierd mod that took the PSU out of the case, and put it on top at the back. This opened the area where the PSU went for dual 120mm fans, and let the PSU have plenty of cool air from outside the case. It also opened up the interior for some extra room and allowed me to get most of the extra cabling completely out of the way...
The only drawback to this 'design' was that it had a rather "ugly" hump on the top of the case... but at the time, looks didnt matter as I was running a dual celery 366 and overclocking the hell out of it...
I also needed the extra cooling because of 5 SCSI HDDs that were nothing more than expensive toaster ovens... 8)