For a posh one try Unicol - no good for boarded walls though as you can't get enough fixings in - unless you drill more holes.

Unless it's an insanely heavy tv you wont have any problems with pb walls so long as you get a good 14+ fixings in Ok so it's not ideal, but it does the job and saves a lot of hassle.

Chris (who used to put them up for a living and generally tried to avoid the above but has resorted to it on occasion!)