Perhaps the most common question at the Remote-Explot forums is.
What USB adaptors work on Backtrack?
Which may either be received with a please Google for the answer or some hostility for not reading the newbie area first.
My aswer to this question is not to ask for just the specific adapter but also for the wireless chipset. Atheros is one of the preferred choices because of it’s open approach which makes them favorable for developer support of various testing tools.
But in my case I am always on a budget and I prefer to but the wireless USB dongles that have the chipsets made Ralink, I will admit that they suffer from temperamental issues please keep that in mind when buying one.
And for an exact model I won an Asus WL 167G which cost me around $25 dollars on Newegg.com. ASUS WL-167g (version 2) later I made some hardware modifications to add an external antenna in order to gain more range.
I suggest you look at the more detailed list provided by Offensive-security.org.