You know all those DVD players that will also play video/music/photo files off of a USB stick? It's one of those, but without the DVD bit. Basically, it's a tiny box (fits easily in the palm of your hand) that you plug USB stick into - and then watch whatever is on it on your TV. It comes with both HDMI and Composite connections (so can be plugged into a SCART input easily with a connector), played every XVID and DivX file I threw at it, and was about two minutes work to set up.
And it's £25 on ebuyer at the moment.
If you're fed up of watching downloaded videos on your PC, and don't want to go through a lot of fuss to watch them on your TV then I highly recommend it - it's fantastic.
Thank you very much to poisonduk for recommending it to me in the first place.