If we are assuming that this HD version of the SD channel, implies that they have true HD versions of the programming, then definitely Fox Soccer Channel. (A lot of their content is broadcast in HD in Europe, so they would have to have a big transatlantic satellite feed leased all the time.)
However, many of the "HD" channels still have a lot of upconverted 4x3 programming, so I think we are still at a point where there ain't all that more HD content out there. For example, I was disappointed to find that Penn and Teller is shot in SD and just upconverted for Showtime HD.
PS If you guys are thinking the new Doctor Who eps in HD, then I'm with ya. But I can't get into Soap Opera Galactica ... and Dresden turned out to be disappointing...