Assuming that you want HD programming, you have no DirecTV TiVo options. Your only recourse is to either get their shitty DVR, which you have to rent, IIRC, or move to cable and get a TiVo Series 3 or TiVo HD.

Well, I suppose you could get a TiVo and hook it up to the analog output of a standard DirecTV reciver, but there's no way to get HD programming that way.

It's also important to note that both HD TiVos currently are CableCARD devices, and that might be a problem if your cable company switches to SDV.