Hiya mate,
Yeah, at that distance you'd be sorted with a 46" or more. If you're thinking plasma that really gives you two options, Sammy or Panny. 3d will be of the active variety of course. Of the samsungs, as vickster says, the 6900 seems to be the one most favoured. It certainly seems to have had less reported problems than the panasonics. All sets have their issues but the last couple of years hasn't been great for trouble free sets.
If you're thinking plasma then my money would be on the 51" 6900. With the shops clearing out last years stock you might also get a cracking bargain. Best of luck