I have just bought an LG 55" 4K 3D LCD TV and must say it's very impressive. It has passive 3D which I purposely chose as we have 3 kids and if the glasses get broken then it's only a couple of quid for a new pair. No batteries to keep charging either.
It cost £1300 and for the money was the best deal for what it can do.
It has a 1000hz refresh rate so no ghosting or lagging. It's great for the kids xbox games and I've just purchased the LG dual play glasses which let 2 gamers playing a split screen game to have both images blended together so each can only see their own game scene, but in full screen.
4K content is limited only to Netflix at the moment but the tv will try to upscale the input it sees.
It replaces a 50" Panasonic plasma, that has nothing wrong with it, and I would've stayed with Panasonic, had they done an equivalent passive 3D version.
The 3D on the LG is very good. It's made me jump a few times
I have also just added an Apple TV box too, so I have full connectivity between iPhone, iPad, tv, and amplifier.