I use this website (as I know many others around here do):
http://www.jacquielawson.com/
It costs £7.25 for a year's membership (or £11 for 2 years) which enables you to send an unlimited number of animated eCards (with sound).
You can click on 'Preview' to see what any of the cards look (and sound) like before you join, so you don't have to commit yourself unless you're sure it's what you're seeking.