I was going to ask the same question. I have a 4200 RPM 2.5" HD in my A500 and it gets very hot - the hottest thing inside the Amiga. There's no way to place the drive any other way than directly on the card and I hate fans.
I need to replace it and want a 7200 RPM drive, but was worried about the heat. I've heard some people say the 7200 drives are no hotter than the 4200 drives, and others say they're much hotter.
Does anybody have any recommendations for a cool 7200 RPM 2.5" HD or is there any way I can search for the coolest one? (temperature wise, not "hey, cool" ;-) )