At the moment, pretty much nowhere because you need a special 3DTV and they aren’t available in the UK yet.
Although, if you’re a PC gamer, you may want to check out Nvidia’s 3D Vision which turns games into 3D.
The broadcaster most likely to launch 3D content first in the UK is Sky, so you may want to check them out. They said their Sky+HD system can already process 3D content, so then you’ll only need a 3D telly!
(update: Sky will be showing Manchester United v Arsenal at a few pubs across the UK at the end of Jan. The 3D channel will launch in April to Sky’s retail customers (pubs etc), but not to home customers until later in the year. When it is offered to home customers it will be a free upgrade to those taking the maximum package of Sky World HD.)
But check back, because we’re scouring news sites and feeds daily. The most comprehensive system so far announced is by Samsung and features a 3D TV, a 3D Blu Ray player, special 3D glasses and Monsters Inc in 3D. But you need to buy the whole package from Samsung.
(update: from a Jan 2010 press release, “Samsung have begun producing LED and LCD compatible panels for 40-inch, 46-inch and 55-inch full-HD 3D TVs using ‘3D Active Glasses’ this month, employing Samsung’s exclusive true 240Hz technology”. So it looks like Samsung and Samsung-relabelled 3D TV’s will be the first ones to market)
(updating as and when)