Multitouch Applications from Falcon4ever on Vimeo.
Multigesture.net is a multi-touch and multi-gesture research blog by Laurence Muller. He developed a multi-touch system called tDesk. He also obtained MS degree for the multi-touch interface. His master thesis is well organized and covers various aspects of multi-touch systems, from system design to user study. For me, Chapter 3: Multi-touch detection and processing is quite useful to understand the internal data processing of multi-touch systems. If you are to make your own multi-touch gesture software, the thesis is worth while to study.