I bought the Eye TV Hybrid for my iMac earlier in the year, and it's been awesome so far -- just hooked it up to a regular old analog TV antenna, but it still managed to pick up tons of digital over-the-air TV and radio stations.
It was also super easy to install -- put in the software, then plugged the little Eye TV USB into the Mac, and everything worked without a problem. Recording TV shows was easy, fast-forward and rewind was easy, programming future recordings was easy, etc. -- not as slick as Tivo, but better than a lot of DVRs.
You can also route cable TV, VCRs, DVD players, etc., through the device -- but I haven't tried that yet. Planning on using it to convert a lot of my old VHS home movies into digital files so I can edit them and toss out the tapes.
Elgato also has some other, higher-powered TV-tuner and conversion products available:
http://www.elgato.com/elgato/na/mainmenu/products.en.html
. . . but the Eye TV hybrid seemed to have all the spcs I needed and was conveniently small in size, so I went with that.
(I actually bought it on Amazon.com, which was slightly cheaper.)
-- Luke