The Hauppauge WinTV PVRUSB2 is a USB tv tuner device from Hauppauge. It has a mpeg encoder/decoder on board which makes it an excellent device for nearly all systems starting around CPU's 1GHZ or above. The stereo audio is excellent. Please do not confuse this product with the Wintv USB2. They are two totally different devices. A link to the product page: http://www.hauppauge.com/site/products/data_pvrusb2.html.
It works perfectly for watching tv as a v4l2 device in mythtv and xawtv. The device's status as supported in TvTime is unknown as of 5/2008. The only caveat is that firmware is required to make the device functional. AFAIK, the firmware is widely distributed and totally legal to download and use in a GPL environment. Search Google with the phrase "pvrusb2 firmware" (no quotes) and you should find a copies of the firmware. The author of the excellent device driver has a site devoted to its maintenance, including firmware extraction instructions should you need them) located at http://www.isely.net/pvrusb2/pvrusb2.html. For debugging purposes, watch dmesg carefully while you plug/unplug the pvrusb2.
It also functions as an FM Stereo tuner. Depending on your kernel version, it may work "out of the box" with kradio or gnomeradio. Check Mike Isley's site for more information.
An HDTV version of the device has been released by Hauppauge. It seems likely it will eventually replace the pvrusb2 at some point in the future. As of 5/2008, both devices are widely available, but the newer HDTV-equipped device isn't widely supported in the Linux kernel yet. Hauppauge reports there will be support for the new device in the 2.6.26 Linux kernel version.