pearLabelizer is a little utility that makes it a breeze to print addresses or other text onto specific labels of a label sheet. It's pretty straight forward to use, and hey, it even supports drag & drop directly from MacOS X's Address Book. Of course you can configure your own label sheets or print addresses for whole groups defined in Address Book too.
Besides drag & drop of text or addresses you can also use a global text view to enter an address, format it and print it on multiple labels. You can select indiviual labels by (command)-click or click & drag to select multiple labels at once.
pearLabelizer also provides a Service-function if you copy it into your Applications-Folder. This allows you to simply select the address in your text editor, choose the pearLabelizer-Service from the Services-Menu and finally all you have to do is select the label on which you would like to print the address.