They make a DVB-T card (the AVerTV DVB-T) which has linux drivers, and a DVB-S card (AVerTV DVB-S) whose status I am unsure of.
There have been some postings on the linux-dvb Mailinglist that some versions of the Avermedia DVB-T cards known as model 761 (with Microtune DTF7072 tuner module) have serious sensitivity problems.
New card revisions called model 771 and model 777 are based on the MT352 Demodulator. These cards work well with the latest kernels (confirmed for at least Australia and Spain). The first few versions of the MT352 driver didn't work so well, so try upgrading if you have problems with tuning. The author (nathanh) has been using a 771 for many months under MythTV. Other autor (Klez) has been using a 777 in Spain with Xine without problems.