I bought a Transcend 4Gb 150X from Amazon for about £27
http://www.amazon.co.uk/Transend-4Gb...219928&sr=1-20 for my Casio and it works fine. Not sure what the difference is with SDHC but they have a 4Gb SDHC class 6 for £7.34
http://www.amazon.co.uk/Transcend-Fl...2219832&sr=1-2. Not sure what kind of reputation the make has but as I said, I've had no problems.
Hope that's some help