I run a blog on what HD is available on Virgin Media (see the link in my signature below). In addition to BBC HD, there are over 100 hours of free HD On Demand content from the BBC, HBO, and the History Channel, plus around two dozen HD movies (under a fiver each - prices vary).
In his last presentation to investors Virgin Chief Exec Neil Berkett announced plans to "add linear HD channels" and "build our HD offering". More details
here