I found the search for a case more daunting than the search for a PDA.
In the end, I got The Holster from Pocket Solutions. I simply wanted something I could clip on my belt, and then remove the PDA by itself.
While I haven't tried it this way, it looks like the strap that goes over the top to hold the PDA in has enough give that you could keep a CF wireless network card installed and not have any problems.
What I like best is that the clip seems very strong. I don't have any fear of this thing falling off.
So, I'm happy with what I got, but I could easily see myself picking up one other type of case and switching between the two based on what the need might be.