Short-term, mid-term, and long-term strategies for a company that doesn't have a Data Backup policy?

The most common backup strategy today, outside of companies that afford a tape robot is external harddrives, usually USB or firewire. This is a very shallow form of backup.

Having one single backup is a problem, as it covers only a part of the failure modes that can wreck your data. Also, if you are using USB in particular, be warned that the USB connection can be very flimsy. Both USB hardware and USB software (drivers) often suffer from "mouse-syndrome", meaning that they have been designed with a simple devices in mind, not with massive flows of data where no bit is allowed to turn.