This article might interest you, if I may plug my own writing: http://hak5.org/forums/index.php?showtopic=9458
This would fit in your pocket and sniff wireless traffic with any Linux tool you're comfortable with. Wireshark, Wellenreiter, Kismet, Dsniff, nmap, tcpdump, etc.
You could use a Compact Flash ethernet card and plug it in, and scan for as much info as you need.