Terry sells them at the cheapest price I've seen: http://arduino-direct.com/sunshop/index.php?l=product_detail&p=96 ($2.50)
Hi Terry! Send me free stuff!
If you're obsessive compulsive and want a layout that meets your personal criteria then you can use a service like iteadstudio/seeedstudio and design your own boards. The price is $25/10 boards if you squeeze the pins to the edges of the board on a 10cm x 10cm board.