I'll add one more opinion, since I don't see it clearly stated anywhere here:
Forget about ZIP drives, they were fairly crappy when they were new and by now I wouldn't imagine them to be worth the trouble.
Wait around for a sidecar SCSI expansion for the A500, I've had no less than 3 or 4 pass through my ownership in the past 3 years. I've had pretty good luck with the SupraDrive XPs. They do seem to be getting a bit harder to find, but short of obtaining something like an IDE68K device, they're probably the easiest way to go (and can often also add some fastram for you.) I'll assume you're not in the US, otherwise I could probably offer a SupraDrive with 8MB RAM at a reasonable cost. Shipping and customs kind of mess that all up, though.
