Power Line Communication
That may not mean a lot to you until you know what it is. Power Line Communication seemingly works by magic.
Problem: You have a wireless router which works with your wireless laptop and your Mum can sit on the sofa browsing on her iPad and your sister can download games on her phone. But your XBOX 360 and your OnLive console which you want to use in your room upstairs – away from the router – and only have ethernet Internet (technically LAN) connections.
Solution: Buy two Power Line Communication boxes which can sent wired ethernet data through your plug sockets – plug one in by your router, one in by your wired device, and connect them both up like you normally would! See? Magic!
Whenever you tell anyone about this, it usually shocks them – I mean theoretically it should work, but in practice, you just can’t see it working very well. In actual fact you don’t get bad throughput – roughly 80% of what you would normally get over a CAT5 cable.
It actually works by using a higher frequency over the same cables the power uses, and the transformers in the plugs themselves take care of the all the differences. You can read more on the wiki page: http://en.wikipedia.org/wiki/Power_line_communication
Even thought they are expensive, they have come down in price a lot from when I last looked. These, for example look pretty good for their money, and they look quite tidy too: http://www.amazon.co.uk/TP-Link-TL-PA211KIT-200Mbps-Powerline-Ethernet/dp/B004INVKP4/ref=sr_1_5?ie=UTF8&qid=1319050256&sr=8-5
Update: Will Derrick pointed out to me that you really should change the default password on the set of these if you happen to get any, otherwise anyone who can actually see them might be able to compromise your security!