I use scrapbookpictures.com. It's not the cheapest option. But, I like to scrapbook, and I can order my pictures in all different sizes (2 x 2, 3 x 3, 4 x 4, 5 x 7 , etc.) plus the regular sizes. If you order larger prints (5 x 7 or bigger) is is much less than Walgreens or some of the other places. You also have far more options for print quality and paper quality.
Also, you upload and store the pictures at whatever size you took them - so it does not "scale down" your print quality. There are no storage limits or storage fees.