A few months back we reported on the Lemur Touch Pad controller in this post. Very cool gadget but it costs several thousand dollars.
Now you can have a poor man's equivalent and Danish developers Livelab's Tablet 2 Midi software could be the next best thing.
The tablet2MIDI uses standard tablet PCs or digitizer, and a cheap usb/midi cable and their inexpensive software (which is still in beta). A tablet PC can be had on ebay for several hundred dollars (e.g. a Fujitsu Stylistic) if you don't have one and digitaizers and pen tablets can be had for about $50.. It will only be mono-touch whereas the Lemur can take simultaneous movements from ten (or more) fingers - but its a start.
"Tablet 2 Midi allows you to use your tablet / digitizer as a MIDI controller. You can define different areas of the tablet surface as different controllers, allowing you to create just the setup you need. The image above shows a 9 channel midi mixer with sliders, buttons and XY pads. Every outgoing midi CC value can be interpolated to get smooth parameter changes."
The Lemur software is a little clucky looking, but it's inexpense. So if you have to have a touchpad control surface, and do not have the resources of Bill Gates, this may be the way to go.