No specific recommendations from me. Check the script repositories for apps that suit your need and work from there. There isn't too much involved, but you can make it as complex as you'd like. Most of these sites now-a-days have flash e-cards that are all flashy and stuff. My suggestion to you is to brighten up on your flash skills if you haven't already :)
Well, two of my brothers and I exchange funny e-cards for our birthdays. If it's within a week or so of my birthday, and the note says "[Name of Brother] has sent you an e-card," I'll trust it. If "a friend" or, even worse, "an admirer" sends me an e-card - no, thanks.