Dave Akerman has used a Raspberry Pi computer board as the flight computer on a High Altitude Balloon (HAB) and sent back live images from near space at an altitude of almost 40 km
The balloon, appropriately called PIE1, was launched from Brightwalton, in Berkshire on July 14, 2012. The images were transmitted on 434.650 MHz (300 bps, 600 Hz shift) in the amateur radio 70cm band using the Slow Scan Digital Video (SSDV) standard.
PIE1 reached an altitude of 39,994 metres and images were received as far away as Northern Ireland (that's over 500km, not bad for just 10mW on 434.650 MHz!).
The full story and pictures are on Dave Akerman's website - http://www.daveakerman.com/?p=592
Slow Scan Digital Video (SSDV) - http://ukhas.org.uk/guides:ssdv
UK High Altitude Society - http://www.ukhas.org.uk/