Since the Sony outputs 768P, you will be best served with a box that outputs 720P natively. There are a few. The first is the Panasonic, but it has a number of flaws. You can search this site for more info. The Samsung outputs 720P, but is not a satelite box. If you are looking for a DirecTV box, that will not work. Dish network's Echostar box outputs 720P. If Dish works for you, that would be your best choice. In addition, there is supposed to be a new box by Zenith released shortly that will output 720P (should have been released around April and the most recent updates on a relase date is anywhere from July to September). The Zenith looks great on paper, but so did the Panasonic.
I also have the Sony projector and decided that I didn't want to wait for the Zenith. I purchased the Mitsubishi box about 3 months ago. It's not perfect, but it works for me. The Mitsu, the Toshiba and the Hughes are essentially the same box. The all output 1080i and then convert to 720P for the projector. I've also heard very good things about the RCA, but it also outputs HD in 1080i. Since I don't have anything to compare it to, I don't know how much better a 720P native signal will look. One of the factors that went into my decision not to wait is the fact that most of the available programming is not is 720P.
Sorry to ramble on. Hope this helps.
-Brett