True USB-powered 1.8" Drives from IOGear & Iomega
 

Hi, we just got news that Iomega and IOGEAR have simultaneously announced the availability of two new hard drives centered on the 1.8" HDD form factor. The new Hi-Speed USB 4200-rpm hard drives are the ones that are truly USB powered since most 2.5" USB hard drives would need more power to start up than USB bus can provide. So, the 2.5" drives usually come with an AC adapter just in case. With these drives, you wouldn't need to carry a power adapter. In fact, the Iomega model in particular doesn't even have AC power hole.

http://www.everythingusb.com/news/index/5528.htm