When looking for a USB adapter for Backtrack 5 or Kali Linux, the main thing to look for is the chipset the wireless USB adapter uses. Here are chipsets known to work with Backtrack 5 or Kali Linux.
1. Atheros AR9271 IEEE 802.11B/G/N
2. Ralink RT3070 IEEE 802.11B/G/N
3. Realtek RTL8187L- IEEE 802.11B/G
The 8187 chipset was good but adapters with this chipset are wireless G and becoming dated, so if possible go with the other chipsets. The following are adapters have been tested and are know to work with Backtrack and Kali Linux.
The following are Backtrack 5 / Kali Linux compatible USB adapters / dongles with Links to Amazon and AliExpress if available.
Adapters that use the Ralink RT3070 Chipset
Adapters that use the Atheros AR9271 Chipset
Adapter that use the RT3572 chipset
Wireless G only USB adapters, Realtek 8187L chipset
The following USB adapters are dongles that were best sellers in the past but since they only support wireless G they have become dated.