I don't have any affiliation with them but thought someone might be able to use this information. I just ordered new business cards from Overnight Prints and received them yesterday. I created my cards in Photoshop and uploaded my artwork. I have to say I'm very satisfied with the job they did and for double sided, full color, and glossy on the front you can't beat the price and I think the quality is great.
There's even a 10% off code available: FEBSALE08
I use the back of my cards as place holders at sales. That way, I pick up the piece and the card and put it in a bag. The customer has my card automatically.