Best portable printer for Ipad?

I will be using my Ipad2 in various locations to create and print out artwork on the spot for clients. Ideally I'd like to find a good portable printer that I could use without having to plug in Airport express since I'm not sure if I'll always be near an outlet.

Since I'll be printing artwork, color accuracy and quality is huge issue, as well as speed. I'm not too good with all of the techie lingo so I'm not sure exactly what setup I'll need as far as apps for the Ipad and the printer to "talk" to each other. I'm getting the Ipad 3g, but from what I understand I would still need to be in a wifi hotspot for a printer to communicate with the ipad?

Any recommendations for a printer and info on the easiest way to set this up would be much appreciated!