Hi, all.
For the aircraft tracking stuff I was showing last night, I used a generic USB gizmo sold for watching DVB television on the PC. I think I paid £12. There are many of these things that will work, but make sure you get one that uses the RTL2832 chipset. More info is available at
http://sdr.osmocom.org/trac/wiki/rtl-sdr
which is where I got the device driver. I then used dump1090
https://github.com/antirez/dump1090
to get the ADS-B messages. Both of these packages built on Raspian with no issues.
For visualisation I used Virtual Radar Server
http://www.virtualradarserver.co.uk
That required a bit of faff. It works fine under Mono but the options dialogue causes it to crash so you can’t make a config file. I’ll dig up the one I created by running it under Wine and post it.
Cheers!