The hack|this blog run by Chris Haralson recently recommended Alfa's AWUS036NHA Atheros-based Wi-Fi USB adapter for Linux users, primarily because it "supports all six wireless modes" in Linux. It is supported in Backtrack 5 and Kali out of box.
Read more on the hack|this blog.
i have been looking for wireless network adapter that supports monitory mode for penetration testing jobs, thank God i found one.