The LaCie MosKeyto measures less than 20mm and weighs 10 grams, making it one of the smallest USB keys on the market. It offers capacities up to 8GB, and becomes nearly invisible when plugged into your computer, and can even travel alongside it in a protective sleeve or briefcase – just plug it, and forget it. Since it lies flush against your device, you’ll never lose it, and there is no risk of damage to the USB port, computer or key if the drive is knocked or bumped. Additionally, LaCie has integrated an extra 4GB secure online storage from Wuala into the MosKeyto, making storage and sharing your files, photos, or videos easier than ever.
I have posted this item not because of price, but because of it's size I have done a very quick search but not found any, but I am sure there will be a cheaper one's somewhere. . . .I know you can use SD cards in lots of equipment but the are many which only use USB and this is discreet ( I hope you find this of interest )