Cheers Morgo.
You could try one of these:
http://redhill.net.au/d/134.php
Jokes aside, to the best of my knowledge, there is no such thing as a "rugged" hard drive these days, insofar as drives are mass produced in vast numbers by only four manufacturers, all with very similar one-size-fits-all products. The actual drive inside your external casing, in other words, will be a stock standard Seagate, Hitachi, WD, or Toshiba model, bought in by the company making the external case and putting their brand on it.
With that said, modern laptop drives (like this one) are incredibly tough and withstand abuse in a way that is still quite unbelievable to this 35-year industry veteran. By putting that remarkably tough little modern drive in a thick, rubberised casing, it will be tougher again. Remember, though, that small, relatively light objects experience very, very high gee forces from even trivial-seeming bumps in a way that larger objects do not - so treat it like eggs anyway!
There can be no great harm in the "ruggedised" model as opposed to any other external drive, but be aware that (so far as shock is concerned) it can offer you nothing at all that you can't achieve yourself as well or even better by putting any other drive in a rubberised casing or wrapping it in foam and sticky tape or even shoving it into something like a pair of Explorer socks. The drive inside is exactly the same, remember, and quite possibly came from the same factory on the same day.
However, the Lacie product might save you hunting around for a suitable DIY protective rubber sleeve, and leave you with a nice, neat one-piece unit. I reckon it comes down to price: I'd pay an extra $10 for it (as compared to an otherwise similar standard external drive), maybe go to $20 extra. More that that would be too much.
Oh, and of course, for shock resistance, solid state drives are by far the best, but (as you know) they are small and very expensive per GB.
PS: the Mark IV
ruLeZ!