I use a Fujitsu C500 which has a nice size 8.4'' screen and can be had used on Ebay for around $150, so it's a great value too.
The wifi connection works via a PCMCIA card that some sellers include on Ebay. I had no problems running the binary orbiter on it under widnows (it uses 98 or 2000 or something).
I did not try network booting it as an orbiter (to try and play music and see if it would do video). Since you can't do this via wifi, you would need a craddle and could perhaps do it with wired ethernet.
It could be nice if someone could find a way to network boot via wired, then have the wireless interface take over so that you can undock the tablet and walk around in the house :-)
Some people have sucessfully installed Ubuntu on it, so if/when disked MDs return, that could be an option too...
EDIT: an important thing I forgot to mention is that the screen only works decently when using the stylus. If you try to use your fingers, you have to press very hard and it's not comfortable. I didn't find how to change this via driver or settings so far