Mp3HolySpirit.com 
This site offers a good selection of free spiritual and Christian-themed greeting cards that offer MP3 music accompaniment. Categories include holidays, love, friendship, thank you, birthday, congratulations, get well, humor and more.

All-Yours Digital Cards 
A major, well-done free greeting card service. Many images are available and you can customize your digital greeting card's color, backgrounds and music. You can even link to any picture and/or sound on the Web. You can also add a sound selection from your own computer. If you have a Web site of your own, you may set up your own custom co-branded postcard service via this site.

Electronic-Greetings
This unique free service lets you easily set up your own custom digital greeting cards service on your Web site. This nifty feature is a great way to add extra appeal to your site and it helps you build repeat traffic. The service works on all types of servers and can be set up in only a few minutes.