This is in response to the post from Stephan Jurgens.
First, regarding free motion capture data. I know of two sources that have files you can download. The variety of movement available is mixed. The first is from Carnegie-Mellon University and is quite extensive, although certainly not focused on dance. They have 1648 trials in 6 categories and 23 subcategories. The second is from Animazoo and provides examples of motion captured with this company's mocap technology - this technology involves strapping instrumentation (goniometers) onto the body.
Carnegie-Mellon University http://mocap.cs.cmu.edu/
I am sure that there are many others who have extensive mocap data that they would be willing to share. But that gets into all kinds of copyright issues. Do a Google search on mocap and dance.
Commercially, my company, Credo Interactive Inc, has a CD entitled MegaMoCap that provides motion capture data for a variety of movements in a wide variety of formats (the problem with mocap is that there are a number of different formats). See http://www.lifeforms.com/products/motion_capture/index.html
We also have a CD Ballet Moves II by Rhonda Ryman. This is not mocap, but rather animations in DanceForms of English ballet sequences accompanied with metronome beats. Ballet Moves II also includes a complete Russian Dance library and selected palettes & motions from the Italian school. See http://www.lifeforms.com/danceforms/
I know others have mocap data available commercially, although it has been a difficult area for companies to see a consistent market.
Without wanting to plug Credo too much, I should mention that our DanceForms (formerly Life Forms Dance) software can easily integrate mocap data from a variety of formats with DanceForms animations. Everyone knows that editing mocap data is difficult - compared to animation the data it is very dense. But with patience you can do whatever you want in DanceForms.
At Simon Fraser University in the School of Interactive Arts and Technology we have been experimenting with searchable repositories of movement clips (mocap and animation). The clips are described with metadata that facilitates a search. We have prototype repositories for ballet and for other human movement. But these are not ready to be released yet - in part because the technology is under development and in part because of copyright considerations.