OWC Mercury On-The-Go Pro: 500GB, Bus-Powered
Officially called the OWC Mercury On-The-Go Pro, this portable hard drive contains a 500GB 7200RPM HDD and arrives in three separate models including a 'Triple Interface' one with FireWire 800/400 and USB 2.0 and a 'Combo Interface' with just FireWire 400 and USB 2.0. The drive itself checks in at just 3.5" x 5.5" x 1" in size and is housed in an acrylic enclosure. Also of note, it's entirely bus powered, so there's no need for an AC adapter.

All three variants work with PCs and Macs and can be ordered right now. Details about the trio are posted below, with prices starting at $189.99 and reaching to $239.99 for the 'Triple Interface' edition.
• OWC Mercury On-The-Go Pro “Triple Interface” FireWire 800/400 + USB 2.0: $239.99
Features Oxford 934 chipset, two FireWire 800 ports, USB 2.0 Mini-B port, FireWire 800/FireWire 800 to 400 and USB 2.0 connecting cables, carrying case, $200 retail value disk utility bundle, and a three year warranty.
• OWC Mercury On-The-Go Pro “Combo Interface” FireWire 400 + USB 2.0: $219.99
Features Oxford 934 chipset, FireWire 400 port, USB 2.0 Mini-B port, FireWire 400 and USB 2.0 connecting cables, carrying case, $200 retail value disk utility bundle, and a three year warranty.
• OWC Mercury On-The-Go Pro USB 2.0: $189.99
Features JMicron 20339 chipset, USB 2.0 Mini-B port, USB 2.0 Mini-B connecting cable, carrying case, $200 retail value disk utility bundle, and a three year warranty.