I work at Upverter, so I've both used it and like it. I don't want to give a sales pitch, but here's some content that might be of interest to the Arduino community:
Arduino Reference Design (Arduino Reference Design by ericevenchick | Upverter), for getting started with Arduino compatible hardware on your own PCB
Arduino Shield Template (http://upverter.com/Alex/8840f66750a0b8b0/Arduino-Shield-Template/), for making shields.
Also, let me know if you have any questions about Upverter.