I was just wondering if anyone had seen a hard drive that was bus-powered (doesn't require AC adapter) that could connect through eSATA, Firewire 800, Firewire 400 and USB? The closest I can come is Lacie's rugged drives, Western Digital's Mac Edition Passport and Iomega's eGo's but they all are lacking the eSATA. Is this just not possible?
What you ask is a bad idea. For a while some external drives were sold with USB connections that did NOT need their own power supplies, because the standard USB port has power available - limited, but some. Especially as hard drives got larger, some appeared with a branched cable with TWO USB connectors on the end, and you had to plug in both to different sockets so that the drive could get enough power from two outlets - one was not enough. Some small external drives - the ones based on 2½" drives and sold for use with laptops -still use this dual connection system. But almost nobody makes cases with 3½" HDD's inside without their own power supply - you simply can't draw enough power from one (or even two) USB connectors.
The eSATA standard has NO power supplied in the data cable. On internal SATA the data and power supply cables are separate. eSATA does the same. So you could not attach an external hard drive by eSATA only - it would get no power. I suppose you could design a unit that communicates by eSATA but obtains power by two USB connections, but why would you? Firewire systems, on the other hand, DO have some power available in the full-size connector, but not in the small one used for self-powered peripherals. (That's similar to USB, which has a smaller no-power-available version of connector.)
You can buy USB-powered drives if you stick with 2.5" or 1.8" drives designed for laptops. Those drives are designed for a battery-powered system so they don't draw very much power. So if you can live with slightly lower performance and a 500GB maximum capacity, they might work for you. I use a pair of these drives for offsite backups because they fit into my safety deposit box. They connect to a single USB port (no dual sockets required) and work fine.
But as Paperdoc says, you won't find any full-sized drives that are bus-powered, and even if you could find one with eSATA you couldn't power it with JUST the eSATA connection.
I see they provide an eSATA cable that adds a USB connection, too - that's how they can make this "bus powered". But they also include a separate power supply as the alternative. Plus, this unit does meet your requirements of an external drive that has all four interfaces available.