I actually used my long-dormant Yahoo! messenger username to activate a Flickr account just so I could order some Moo Minicards. They’re US$20 for 100, including free international shipping.
Business cards are a great promotional tool, and especially useful as a distracting device when punters approach you mid-set. I have a couple of designs for different occasions, but Moo’s double-sided, full colour cards seem much more relaxed and friendly.
The Moo Flickr Group contains plenty of action shots and positive feedback.