Valve's Steam Link box (which lets you stream your PC library to another TV or monitor in a different room in your house) is cheap as chips right now, going for a mere £2 / $2.50 in the Steam Intergalactic Summer Sale. That's a whopping 95% off. It would almost be rude not to, really.
Admittedly, UK buyers will still need to pay a hefty £7.50 postage and packing fee on top of those two British pounds, making that great deal slightly less great, but that's still a heck of a lot better than paying £7.50 on top of its regular price of £40. Of course, you may not even want or need a Steam Link now that you can do it for free on your Android phone / tablet (sorry iOS peeps), but sometimes you just want a nice big juicy screen to gawp at, which is where the dedicated box comes in.
It's certainly more convenient than lugging your entire desktop PC and its nest of cables into your living room and connecting it up to the TV whenever friends are round, but as Alec has noted in the past, its streaming can get a bit wonky in terms of control response if you try to stream over your home Wi-Fi network. Indeed, Valve themselves recommend using a wired connection, so it may be worth investing in a pair of home plug adapters (around £25 in the UK or $40 in the US) if your TV isn't anywhere near your router. That, of course, is yet another extra cost to consider, but home plugs are pretty handy to have anyway - especially if you have a PC upstairs that's also miles away from your router.
You don't need to buy a Steam controller for it either (although there is a nice Steam Summer Sale bundle going on anyway that saves you 66% off its usual price), as the Link box plays nicely with most common PC game pads, including wired Xbox One and Xbox 360 controllers.
This deal will continue throughout Steam's Summer Sale until July 5, so there's no need to rush out and get one right now, although the sooner you hit that purchase button, the better, as Valve have already indicated that high order volumes will probably result in delays getting them sent out.