I ordered Christmas Cards from Costco today. Their 6×7.5 cards were reasonably priced at 50/$14.99. I used their templates, although I did note that Costco also had the ability to create your own card and upload it. For this project, it was easier to create the project online, and they had a wide variety of templates available. The only disadvantage is that I have to settle for a relatively low-resolution screen capture to illustrate this blog. The order even came with four free calendars.
Note added December 9, 2013: Costco’s 6×7.5 photo cards are printed on Fuji Crystal Archive photographic paper. The quality is high and I would recommend them to anyone looking for high-quality cards at a low cost. As others have commented, Costco also offers press printed cards that allow both sides to be customized. I have not evaluated these cards.