I recently bought about 3.5GB worth of memory cards from a company and the prices were incredibly low.
Three cards were bought in all from a company and the link is
www.mymemory.co.uk if anyone wants to try them. I've had no problems with any of the memory so far and the site also allows you to check if the memory you're choosing is compatible with the device you intend on using it with.
(If direct links to other sites aren't permitted then apologies)