Free Postcards
Here are several sites that offer free virtual postcards:

PoochiePicks - Cute virtual postcards featuring dogs and puppies. Your own pet can be selected for use on PoochiePicks. Your own pet can be a star!

KittyKards - Cute virtual postcards featuring kittens and cats. Submit your own pet photo and let your pet be a star!

Glidercards - If you don't know what a Sugar Glider is, you should at least take a look at this. Sugar Gliders are exotic pets and are absolutely adorable.

SpecialtyPostcards - Virtual postcards and printable cards. There are some birthday, anniversary, and other general categories, but the focus is on pregnancy. There are cards to announce your pregnancy, tell your husband, tell the folks and more.