The Lacie Ruggeds have always seemed impressive in terms of physical construction, but I haven't yet invested in those. I have a large collection of drives in various 3rd-party cases: some USB-only, some USB+FW400 (with dual FW ports for daisychaining).
For most of last year I had one or two drives rocking around in my satchel, and they were fine. I did put them in the zip-up neoprene sleeves that are around for such things (the WD Passports seem to come with reasonably thick versions, but they don't fit some of the beefier combo-interface units: I got some other sleeves from somewhere).
I have had one failure, which was a few months ago as I was getting out of my car on a dark night with my satchel in hand. I heard a nasty "crunch": the drive in its sleeve had fallen less than a metre onto the road, and it didn't bounce in a good way... The drive was in an aluminium case, and the plastic mounts at the end of case were cracked (I had to tape it together) but when I got inside I hurriedly tested it and managed to copy the entire contents to another drive. It was a good thing, as I had ~20GB of new files on there...
The drive started failing two days later, but I was expecting that so didn't lose anything. It was a reminder that I need to backup each drive before travelling! Of course the backup drives are carried separately...
Today I tend to carry the drives in these:Case Logic Compact Portable Hard Drive Case with Hard Exterior
Oops, Adorama's down: try the Case Logic page
There's an elastic strap that holds the drive in one side, and a pocket on the other side for a small cable. Unfortunately a drive as thin as a WD Passport won't be held very securely in the strap, but I put two thin drives in each case and it seems very robust so far. I'm not planning to do any destructive testing though...
The cases are also a convenient size for carrying portable backup drives such as Nexto units.
No one's mentioned the Fortress
drives. Does no one use them? Moose Petersen seems to love them, and the sales pitch certainly sounds impressive. But the price premium (and the max 160GB) has kept me away for now.