Hard drives:

IBM SCSI HD

Seagate Hawk 2 GB

x2 Seagate Hawk 2.1 GB

or you can buy a cheaper large 68 pin HD (which are much easier to find cheap than native 50-pin hard drives) (example) and use a converter (example) with it.

For Zip drives, this one is nice.

If you can though, try to find a Zip 100 Plus, as they are compatible with both PC parallel ports and Mac SCSI ports.