I use 2.5" SCA drives in my 68k Macs. They are (or were) available very cheaply on ebay, and you can get adapter boards for a few bucks that convert them to 50 pin SCSI. I like the 2.5" type because they're much quieter than the 3.5" which are almost all 10k RPM. Most of mine are 72GB drives but only have a few 2GB partitions. It's pretty hard to make use of even 2GB of space on such an old machine.
