Scratch (2001) is a documentary film, directed by Doug Pray, that looks at the birth and evolution of hip-hop disc jockeys (DJs), scratching and turntablism.
Interviewees include:

Grand Wizard Theodore (the inventor of the scratch)
Grand Mixer Q-bert
Grand Mixer DXT, Z-Trip
Mix Master Mike
Rob Swift
DJ Premier
Afrika Bambaataa
Jazzy Jay
Cut Chemist
NuMark
DJ Craze
DJ Shadow
DJ Babu
DJ Krush
Madlib
Peanut Butter Wolf

You can watch the whole [...]

yarglaaaafr freestyling on the Nintendo DS using a preview version of his project “ProteinDS”.

This video, by Livid Instruments, shows scratching with Percussa AudioCubes:
I set up four loops in an audio looper program I’ve been working on for future release by Livid Instruments. I’m using the speed of my hand gestures as detected by the four distance sensors on the audio cube to change the playback speed and direction [...]

A demonstration of ammobox, a new free virtual instrument that lets you scratch audio by triggering samples asyncronously with MIDI. The turntable provides velocity and rotation control.
Creator Nathan Ramella (aka Synthesizer Patel) says:
What you see on the screen is me dropping MIDI notes into an Ableton Live MIDI loop, as each note is hit, it [...]