Another really great printer for prints in bulk would be JAKPRINTS @ jakprints.com. They do a LOT of printing for low brow artwork from a LOT of famous and up and coming artist as well... not to mention stickers and apparel as well!
ComiXpress (my favored one and I can be used as a referral for a 10% discount on your first order) Ka-Blam (decent quality) Lulu (better suited to books, can be expensive) Lightning Source (no personal experience with this one)
Lots of people just print their art on something less bendable than paper. Then they laminate it, punch a hole in it, and loop a keychain chain [or whatever they're called] through it. It doesn't look very permanent though.