quite a few Atheros 802.11n devices. See the athn(4) manpage for a
list.
This port has only been tested with a TP-LINK TL-WN722N USB adapter
which has an AR9271 chipset (VENDOR: 0x0cf3, PRODUCT: 0x9271). The
BSS, Monitor, and HostAP modes all seem to work on that adapter,
though the later has not been tested much.
The driver also supports PCI and CardBUS devices, but those interfaces
are completely untested and probably won't work at this point.
If someone can provide me with other adapters that should be
supported, particularly PCI or CardBUS adapters, or tell me where I
can get one cheaply, I would be happy to try to get the driver working
on those devices as well.
christos