Moo.com has to be the best printer on this earth. Their site, moo.com, let's you customise business cards, mini business cards, postcards, stickers and various other things with your own designs or a huge selection of cool pre-loaded designs on the site. So they're a bit desgin-led (with their cool branding, boxes, sizes/shapes and general look) and a bit DIY because you can do your own design and use the cards for myriad other things (place holders, gift tags, etc.).
Plus, the price is right at $20 (or quid in the UK as they now have both a US and UK outpost), the quality of the card stock is wicked (thick and matte which is infinitely classier than thin and shiny) and they show up in a beautiful, minimallist white lacquer box so they look beautiful being stored as well. This is my last set of cards before taking my married name, Jessica Teas, and as a mini-wedding gift to myself, I bought one of their snazzy card holders (which hooks right onto your key chain). See my newest set of Moo min cards in this image gallery, complete with card holder, front and back shots and box.