At the moment the record seems to be held by Sharp, who brought out a 90 inch LED screen in September 2012, with the highest possible HD quality. This will be available from summer 2013.
Another monster screen is from Sony, who brought out a new 84-inch screen in August 2012. The new TV is in 4K, which apparently is much higher quality than HD and has only previously been used in cinemas.
The TV also has 10 speakers, and basically should give you a very similar experience to being in the cinema, but without the popcorn or annoying neighbours! It should be on sale in time for Christmas, too.
There are a couple of drawbacks - one is that most of us don't have a room big enough to house a screen that size. The other is that it is currently going on sale at £20,000.