You need a PCIe wireless card with an Atheros chipset:
There ae no other good solutions at this time.
We sell them here (and 25% of the profits go to help the Trisquel project):
http://libre.thinkpenguin.com/
There is a broadcom card that is free software compatible although I would
not recommend it. Unless you had that and it worked for your only option is
to replace.
The other alternative is to get a USB Realtek card (2nd best choice).
RTL8187B, RTL8187L, and RTL8187 are all good chipsets for general Internet
use. We also have these. There is also an AR9170 atheros chipset which we
offer for N USB. It is ok from a free software perspective too. I'd only
recommended it if you wanted to setup an access point though. There will
hopefully be (we're working on it) a new Atheros chipset for USB adapters in
the the next several months.
