I did a Joe Black on white card, but I left space on the back: Each card is drawn on, or better, it has an original drawing on each one, a sketch or ink drawing of some sort. Like that people get it, and will want to keep this little doo-dad of work for themselves.
Plus it's fun for me.
I have to do a BUNCH now for SDCC (I'm going!) to hand out. Keep a look out. I wish I had more to show but I passed out all the cool ones recently at a gallery show and when I was in SF.
If you're wondering where's the e-mail, I write it on there, since I use 3 different ones for different businesses.