I was a big fan of the 3E "environment" books such as Stormwrack, Sandstorm, and Frostburn - they generated many exciting hours of adventures. Has anyone taken a shot at updating these to fit into the 4E rules, or seen any content designed natively for 4E that fits into this category?
I have seen the Dark Sun rules for travel, and they could indeed be adapted to other environments. The basic framework of sun sickness looks to be very flexible.
Dark Sun contains extended rules for desert travel and the related effects. I haven't seen these yet but they could might be adapted to fit in other environments.