The only wifi keyboard I know of is this android app:
WIFI keyboard
You can sit at your computer and type into a browser window that enters the text into your adroid device. I haven't installed it because if I'm going to sit at a computer to edit text, I might as well just plug the stupid thing in and edit the files directly. I don't really see the point, but it does exist.
I don't know of any standalone wifi-based keyboards. They're all bluetooth and IR, aren't they? The USB ones won't work because there's no USB host on these devices.
However, the thumb keyboard
HERE is not half bad. I use it for entering a few sentences here and there. It has multiple layouts you can choose from, and it has directional arrows to move around inside text boxes. For real writing, I want a real keyboard, though.