PCTV Systems nanoStick T2 290e
It has experimental support since May 2011 in the media tree Git repository for v2.6.40.
The current Linux driver presents two frontends, one for DVB-C, the other for DVB-T/T2. T2 multiplexes are automatically detected and provided through the same API as DVB-T, giving maximum user-land compatibility. Support for T2 specific features are in development, but it's unclear whether broadcasters are making use of such features.
DVB-C does not seem to be fully supported with Linux, especially QAM256 (Windows officially only supports DVB-T and T2), according to mailinglist DVB-T2 LNA(?) damages DVB-C signal.