There was a report, a few months back, in one of the PC mags which compared different brands. The results showed that there was very little differnce between brands.
Cheap SD cards are very easy to come by: Try Jessops or Tesco but, for a recommended UK online supplier go to http://www.xlshop.com. (Current prices: �6.89 for 64Mb, �13.89 for 256Mb, �21.49 for 512Mb).