I spotted this in my local Game just before Christmas. Its still £12.99 online.
Even though this is Game's own brand, it should work just as well as the official Nintendo RGB cable (sells for £20).
If you are still using the cable that came with your Wii, I can really recommend that you get one of these. It gives you a far superior picture than the supplied red/white/yellow composite lead.
All you need is a RGB scart socket on your TV. If you have 2 sockets on your TV it is very likely that one of them is RGB.
If you have a HDTV I think they were reduced as well - but you would need to check.
Loads of reviews of the official lead on amazon here: http://tinyurl.com/2juej9