I figured out the Garmin GPS18 USB issue with some assistance.  All that's needed:

modprobe garmin_gps
mount -t usbfs none /proc/bus/usb

and it works a treat.     But, to the OP who was wanting gps/hw recommendations, as someone who's lived in a car for wireless engagements for a few days, you'll really appreciate having something that you can get working via bluetooth to have one less damned wire making the laptop hard to move around.  :-)

Andrew,

how did you get on with sorting out a GPS unit?

hello!!
bonjours! to say to you that ZIONCOM WL0162 and really definitely! but it works on BACKTRACK or not? and on Aircrack-ng also?? has tested you? thank you for your reponse

Yes, it works fine.

Hello All,
I am looking at upgrading to a new card from my ubituiti 300mw b/g card. I have the AIRNET 300Mb 802.11b/g/n USB adapter in mind. It runs on Linux and uses the Ralink chipset which is injection compatible with aircrack. Has anyone used this device for Wireless Pentesting? let me know. here is a link for the specs

http://www.netkrom.com/prod_airnet_300mb_high_power_usb_adapter.html

Thanks
izman