I'm a huge fan of the 3.5" MO drive. They range from 128MBs to 2.3GBs in size, come in SCSI and IDE, and work on anything from System 6 through OS X, and DOS through Windows 7. They're awesome! I used Anubis utilities to format a disk with Apple drivers, and now I can boot off it as an emergency disk. I put the whole Apple Emergency CD on it.