Modern Postcard is the bee's knees!

I recently used Modern Postcard for a freelance job, and I must say that if you are considering printing anything remotely postcard-like, I highly recommend them, highly. They have templates and instructions for every computer graphics program known to man (and if you can't design it, they can do it (but I can do it for less)). Anyway, they think of everything. If you or your designer follow their instructions, you will have high quality postcards in no time. They even provide postal guidelines to ensure you don't put anything where the post office wouldn't want you to. Even if you don't need the minimum quantity of 250, you will be so impressed by the quality that you will want to wallpaper your house with them. They do postcards in several sizes and styles. They do business cards too!