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 and drop directly from Mac OS 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 and 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 and 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 to select the label on which you would like to print the address.