Any 50-pin SCSI drive will do, as well as any that can be converted to 50-pin such as many 68-pin SCSI drives. So as long as you can get a 50-pin parallel SCSI connector out of it, you can use it. Note that some very fast drives may not reach their peak performance due to controller limitations of these older Macs.

Also, make sure that your drive doesn't run too hot. A 7200rpm half-height drive I installed in my 7300 once died a rapid death due to heat -- it could just fit, but it couldn't ventilate. So stick to the conventional third-height size.