I use the digikey item mentioned earlier (it's on page one... I clicked on the wrong reply), and a wireless Logitech keyboard from Walmart. It was just plug and play on the Maemo side. I could even alternate between the built in and the wireless. I didn't even have to worry about keyboard layout (I modded the rx-44 file to get pipe, curlys and whatnot).
Only issue is that something in EasyDebian (possible the Xephyr binary) doesn't want to play nice with multiple input devices. So there, I have to pick one keyboard layout and live with it.
Ya know, I know you've already got the usb keyboard, but I tried one myself and found I didn't like it, it made the tablet flakey, and it didn't want to play nice. So I ended up getting this BlueTooth Palm Wireless keyboard, and aside from a slight case of user issue when I tried to pair it to my tablet (I need to learn to read directions better. ^_^;; heh.), it connected perfectly and worked great. In fact, it feels pretty natural, and is almost as comfortable to use as my regular keyboard.
I recommend the same keyboard, very easy to configure and use, take small place when folded, and has a very good battery life.
You can find it on ebay.
