The Alfa AWUS1900 is a nice model, but if you want something cheaper (and will put up with 2.4ghz-only), the TP-Link TL-WN722N is cheap, but get the v1 chipset! It's the best-supported with drivers on linux. Oh yeah, and you will probably need to do monitor mode on linux.
Not sure if it is what you are looking for but this site has various products regarding tapping, sniffing and pen testing.