Thermal label printers give a real productivity boost if you ship more than 10 parcels a day. Thermal printers provide an easy to use peel-and-stick label that goes on just about any parcel (and express letter).
In many cases the shipping carrier will provide the label stock at no charge, so the only real hurdle is getting the label printer itself. Several models of printer are supported, including these:



Eltron / Zebra Orion
LP2844 (via parallel port and USB)
Note: eBay is a good
source for a used thermal printer for a reasonable price (often under
$100).
It is not supported to attach a thermal printer to a
serial port.
Next: Installing a thermal printer.