If you are looking for a bargain then take a look at the Moleskine Style iPhone Cover for iPhone 4, 3G & 3GS. It was £9.95 and is now reduced to £6.95.
Moleskine Style iPhone Cover for 4, 3 & 3GS.
Perfectly slim and does not bulk up your iPhone, just slim protection!
Matches your Moleskine Notebooks and Diary. Allows for iPhone camera and flash.