Luke Wroblewski, ever a hero of the design community, has posted some useful resources about touch gestures on his blog:

Touch Gesture Reference GuideThe first resource is a Touch Gesture Reference Guide containing "1) an overview of the core gestures used for most touch commands 2) how to utilize these gestures to support major user actions 3) visual representations of each gesture to use in design documentation and deliverables 4) an outline of how popular software platforms support core touch gestures."

Thanks to Luke, Craig Villamor, Dan Willis, and Jennifer Rhim for putting this together and making it publicly available.

The second resource is a roundup of the multi-touch gestures and diagram styles used by a number of different design groups on a range of input devices, including Apple's multi-touch trackpad and Magic Mouse, Windows 7 for multi-touch, Wacom's Bamboo device, and others.