The net of this is that you probably want to buy your USB Adapter from either thinkpenguin.org for general intel linux and from modmypi.com or adafruit.com for Raspbian. Be careful that there are lots of knockoff cards and things that don’t work:
Be careful when buying a card for this project: – WLAN cards documented as Linux-supported often become no longer available. As a common cost-cutting measure, wireless adapter manufacturers will revise an existing product’s specifications, substituting a different chipset (or other components) without changing the (formerly Linux-compatible product’s) model number. Naturally, this is a common source of confusion for individuals attempting to purchase a compatible adapter, even when they think they know which adapter to buy. Manufacturers don’t help matters much, often using strange naming conventions that produce numerous confusingly similar model names and numbers. Consider: At one point D-Link offered 3 different revisions (with 3 different chipsets) of its DWL-520 adapter, as well as the (completely different) DWL-520+, which was not to be confused with the entirely unrelated DWL-G520, DWL-A520, not to mention the 8 varieties of product offered under the “DWL-620” moniker. Thus it is crucially important to pay close attention not just to manufacturer/model names, but also revision numbers (if provided), chipsets, included drivers, etc, as well. (If uncertain, consider purchasing from a retailer who offers a “consumer friendly” return policy, so the product can be returned/exchanged if it turns out to be incompatible.)
There are very few 802.11N USB adapters with chipsets that clearly support master mode on free software platforms. The situation is rapidly deteriorating as chipset manufacturers have not released source code or specifications in many years. One place to purchase a compatible adapter is http://www.thinkpenguin.com/. http://linuxwireless.org/ also maintains a list of adapters and information on master mode compatibility. This list can be very misleading as most adapters which had a compatible chipset have been long discontinued.
via WifiDocs/MasterMode – Community Help Wiki.