SMacTech, Those thermal printers are close to what I had in mind but none of the ones on your site are portable. I need something that will run on battery, USB, or firewire. I think I'm going to have to settle for a regular portable printer and print full-page invoices/receipts instead, I haven't seen a really portable thermal printer anywhere.
dennisbolt, I've been using an excel sheet with some calculations for checkout math, but I'm working on a Java program that will be easier to use and will help with tracking inventory sold for the day. Excel gets the job done, but the interface is poor for working with quickly and it doesn't produce a nice looking receipt.