Those things which mean you can run a network connection via mains power outlets.
http://www.amazon.co.uk/Solwise-85Mbps-Homeplug-Adapter-Twin/dp/B002XL6IUU/ref=sr_1_2?ie=UTF8&qid=1309174794&sr=8-2

Has anyone had any experience using these?
My router is in the living room, though my study is on a different floor and the wireless signal isn't great and prone to dropping out, these seemed like the simplest solution.