Perhaps the most popular cameras are the Canon brand as many of them can use the CHDK program to do useful stuff! You might want to have a look at this guide as well. Krzysztof is a member here.
I recently purchased a Canon A495 for aerial mapping. It was reasonably priced ($75 shipped via Amazon), and is compatible with CHDK. As covered in other posts, you can trigger the APM relay at waypoints via Mavlink in Planner. I'm setting it up with a CHDK script to trigger the shutter when it receives a 5V signal from the relay via USB. By reviewing telemetry it should be possible to have some idea of the aircraft's location at the time the picture was taken. Not sure about the feasibility of this on Paparazzi though...
Canon PowerShot S95 is also a good option, but a bit more expensive.
The canon SD4000 has been very good to us, even though it doesn't have a finished chdk - we just tape the trigger down. Batteries last 40 minutes or so. I expect the Elph line will be able to do the same. Make sure you get one that uses a CMOS sensor to achieve video capability, though - the CCD sensors are very slow in continuous mode.
At this stage, I would also consider a mirrorless camera like the NEX-5N if you can afford to lose it.
I recently purchased a Sony WX10 for aerial photography. I already have a DSLR, but modern high-end P&S camera are so good, I really don't see the point in going with extra complexity required to lift a DSLR.
The photos from the WX10 are BETTER than those from my Canon Rebel XT with the kit lens.
thank you for all replies. I used the skywalker for the platform. anyone try Replay XD 1080P Pro mini ?
Ricoh G700SE, built in intervalometer (down to 5 seconds), gps module addon writes location info directly to EXIF header! Alternatively Canon point/shoot + CHDK.