I had the same issue as you - so I explain here what I did. First of all go to remote-exploit Wiki -> HCL -> Wireless and read carefully through it.
There are 2 problems:
1. latest WiFi cards available in shops in my area are not on the mentioned list.
2. if you check on ebay (or local Polish auction site equivalent in my case) - descriptions on the web give you general type information without detailed chipset information.
what I did is I printed out the list above and went to "computer parts flee market" which takes place every week in my area.
finally I have chosen edimax wifi card with chipset ralink EW-7318USG that can be handled by rt73 driver under backtrack.
it runs perfectly including monitor mode and packet injection.
it has two further advantages:
1. it has antenna connector so you can buy separatelyand connect long 12dbi antenna.
2. it is USB device so it runs also in VMWare backtrack under windows. (not using this mode too often but still it gives you some flexibility)