There is a major difference between using a professional photo lab vs ordering prints at your local retail store on the 1 hour photo machine. Yes, professional labs cost a little more, but you get what you pay for. I personally use a professional online printing company called White House Custom Color. They are very reasonable in their prices, and when I order prints they are of the finest quality that I can get. They use software called ROES which actually calibrates my prints to their printer, so I know that I will get the best prints possible. Using a 1 hour photo lab at Wal-mart, Target, CVS or Walgreens may get you a decent print to put on the fridge, but it's not going to have the same quality. If you're putting a family portrait on the wall or printing wedding photographs, you should seriously consider the investment and importance of getting a high quality images since it will be a focal point in your house or family photo album. Since I take high quality professional looking photos, I want to see my work displayed at it's full potential. I used to order family photo books from Shutterfly.com, and looking back I'm disappointed that their machines are not of a higher quality for an online printing retailer. My prints always looked much darker and pixilated than what they really were.
Every photographer always has a source for their printing, in addition to White House Custom Color I also recommend Miller's and Bay Photo for your professional printing needs. I've heard nothing but good reviews. If you are going to take your prints to a retailer, I've heard Costco is the best because they have nicer photo machines and offer a great price.