Corsair just announced the latest in their line of USB drives, the Flash Voyager Mini. Smaller then a quarter, the mini is just the right size to lose when you really need them, and come sizes ranging from 4 to 32 GB.
I actually like the Flash Voyager line, and these look interesting as well. The Mini features a retractable connector (instead of a cap that always gets lost) and is (at least physically) very small. They are available now from various retailers, with the 4GB version selling for around $20. The 16GB retails for around $50, and the 32GB doesn’t appear to be available yet. Check out Corsair’s website for more information.