GenGisCAD is a free one for CAD files. It seems much more impressive on the site than I managed to achieve on my Jornada 720 or my Pocket PC, for that matter.
I got it to run, but so far it's too quirky for my CAD uses. It's possible my drawings are too intricate. It needs a new AGYSHELL to run. It's default language is spanish and the menu option to change it to English get's hidden when it starts. I found an AYGSHELL that allowed me to make the change, but it was a lot of work and the end result wasn't satisfying for me. I kept it though. I Plan on experimenting more with it. The manual is a must read.
I think the project is abandoned. I've had no responses to emails or my attempts to register the software. The last updates were in 2002. It opens DXF.
http://www.aptop.com/html/english/procad_e.htm