Amazon and Tivo have hooked up Amazon’s Unbox service to download videos directly to Tivos. They give you $15 to try it out, and the setup was trivial. Sounds like it does less than HD quality for Series3 owners based on the Tivo FAQ saying,

Unbox videos watched on a TiVo are of better quality than videos recorded at the Best Quality setting on a TiVo Series2™ DVR.

Buying movies this way seems a bit limiting between their rules and having playback tied to a Tivo. The list of rentals are a little thin at the moment, unless you are dying to see K-PAX or You, Me and Dupree. But I’m sure the selection will in over time, and the relative speed (vs. Netflix) could make it attractive for a missed TV show or an occasional movie rental.

Update: A comment on Engadget says HD is coming once they re-encode the content. Cool.