Espon. HP, Canon I think all of them make a edible ink, and the cartridges are refillable and not expensive. www.123refills.net FSA
I know Canon make edible inks and are very popular as they are compatible with a lot of there printers, however make sure when you change your inks over that there is no contamination with the old ink as this may not be edible.
Agree with TCC. You don't want to accidentally mix the non-edible inks with the edible inks. You can ask your local cake store for some tips on where to get the best and the cheapest edible inks.