We've seen awkward attempts at external Serial ATA thumb drives before, but they usually needed power from an auxiliary USB connection. Kanguru's new e-Flash drive (PDF) is a different specimen: it has an eSATA plug on one side and USB on the other, but it's designed to work with powered eSATA connections. The USB side only serves as a backup in case there's no powered eSATA connection around.
Kanguru claims the 300MB/s Serial ATA interface delivers five times the performance of "standard USB drives." The company packages this offering with an internal powered eSATA bracket, which apparently adds a powered eSATA port via PCI, as well as a powered eSATA cable. You'll also find HotSwap! software for "trouble-free hot swapping" in the box.
Kanguru's site quotes a $69.95 starting price tag, but clicking the "Buy Online" button only shows $119.95 and $199.95 offerings. The former has 32GB of capacity, while its pricier cousin packs 64GB.