I am looking for a 802.11n wireless card that Linux supports that can be dropped into AP/master mode.
I would prefer PCI, but USB would be tolerable, just not preferred.
Most wifi station cards do not work in AP/master mode.
However Atheros cards do..
PCI Express Cards
All Atheros PCIe cards should be operable in AP/master mode. ath9k supports master mode, so all cards that are supported by ath9k should work in the AP/master mode
Just in case someone stumbles on this -- Using the Atheros pointer that freethinker gave me, I managed to find the TP-Link TL-WN951N
Which has an atheros chipset and someone wrote a tutorial about the very card and master mode.