Kingston is probably the leader in flash drive. The fact that they keep on experimenting with the design makes them very popular and the results are that they have a design to offer for everyone.
If you are looking for an ultra portable flash drive which is so small that it can actually be used as a key chain then Kingston's data traveler mini is your hero. It's of has a length equal to the diameter of a coin. And this little wonder can carry 1 GB (comes in n2 GB as well but mine is 1 GB) of data.
The portability doesn't end on the size. Kingston has bundled a software with it know as "My Migo". Upon installation, this software syncs the flash drive with you're my documents folder on the computer. Thus you can carry your documents with you in the flash drive where ever you go. I tried using the software with another flash drive which wasn't from the migo line but it didn't work, meaning it is only for the data traveler mini migo edition.
The small size can be a problem if you happen to be a clumsy or careless sort of person. At times, it's hard to find it even in the pocket! So it would be better to chain it to a key or a necklace.