Becky was kind enough to include me when she mailed out the moving announcement she ordered from me on etsy.com. She got them printed as postcards at vistaprint.com and I think they turned out really well.
Vistaprint is where, as a super cheap person, I get most of my personal printing done. They screw up sometimes (too dark, trim lines off, etc.), but they are quick to refund or credit or replace, and at the price they charge, it's not hard to overlook the occasional mess up. I wouldn't recommend them for wedding invites or anything you're hoping to majorly impress with, but if you're ordering a couple hundred of something (like a moving announcement), you can walk away paying for almost nothing but shipping if you play your coupons right.