Before everyone votes cold - Class 6 means it's fast - not as fast as the Sandisk Ultras, admitedly, but still much faster than most stuff on the market (min write speed of 6 MB/s being class 6) - If you've got a slow camera, or a SatNav that seems to take an age to do anything this might help.
Use the voucher "FREEDELIVERY" to knock £2 off the price (the delivery is still £1.99 - so actually you save 1p)
Click here - http://www.quidco.com/visit/3288/ZNX/cashback/
- To go to CDiscount via QuidCo for 4.5%
Just to make this clear - this is an SDHC card - your device must support SDHC for this to work!
Next cheapest is 7DayShop at £5.99 - I've bought 2 so far and they've worked great.