A friend recently sent me an eCard from http://www.ze-card.com/. It was great! The print was of Mary Cassatt's "A Cup of Tea" (in the Friends section). There are a number of art prints on this site. It's really quite fun to browse.
The cards are free. The only downside is the flashing advertisements. Be sure to turn ON your popup blocker, as well!
I think I will be using a number of cards from this site. Enjoy!