I have gotten very good results from a TB-Link TL-WN822N USB adapter on my
Mythbuntu system. The system gets its video feed from ethernet-connected HD
HomeRun tuners.

Another option may be ethernet-over-power-line adapters if your computer has an
ethernet jack. I think it may offer more bandwidth than the USB adapter. We
are using a pair of these to connect our TV to the router. These devices can be
sensitive to which phase of the power line they are on.