Thanks to an awesome deal I got through a friend this spring, I now have a second TiVo HD, and I'm using it in the bedroom on my non-HD TV. The TiVo HD works fine that way; it's capable of happily recording either HD or standard TV, and displaying either on an HD or standard TV. It does all the thinking about how to display what it needs to display. So, even if you think "I don't need HD," this is a good option. The TiVo HD uses CableCARDs to tune in the channels you're entitled to view on cable, without the need for an external cable box, and it can record any two shows at the same time without restriction.
(They also have a refurbished TiVo Series2 Dual Tuner for $49.99 and their excellent wireless adapter for $39.99 at the same page.)