Moo is a printing company that makes business cards, mini cards, postcards and more. These cards are super easy to make, especially if you already have photos uploaded to flickr, smugmug, facebook, etsy, or bebo. Simply choose the product you want to make, put your photos and contact information into their templates, and you're done. And the prices are extremely reasonable: 100 cards for around $20.
I made the mini cards (100 for $19.99 + shipping). I chose 20 different photos from my genealogy collection, which gave me a wide selection of cards to hand out. I put my name, email address and two websites on the back. Others might choose to put their phone number, twitter or facebook IDs, etc. Here's how mine came out (the photo itself is a little dark, not the cards themselves):