With the arrival of ESPN and BT Sports 1 and 2, we now have 49 HD channels on Virgin Media. What should be 50th? My vote would be for Sky Atlantic (yeah, I know, "change the record, Nialli").
UPDATE: How wrong am I? Turns out we already have fifty, as something called as NHK World HD is available on Channel 625 (XL pack). I've never watched it as I never venture through the 600s in the channel listings.