I’ve been long time searching for a card or USB TDT HD compatible with all three main Operating Systems I use and in the end I found it, is the WinTV NOVA-T-HD:
It works perfect both on Ubuntu 10.10 and OS X 10.6.5 just plugging in, you don’t need to setup anything. I didn’t test it on Windows but drivers for it are included.
Within Ubuntu I use it with “Me TV” (sudo aptitude install me-tv).
On OS X you only must to install Eye TV and it will work like a charm (this is the hardware that is into famous Mac compatible dongles “elgato”).
I bought it on a MediaMarkt for under 50€.