Hills are among the most basic sort of terrain you need for a wargames table. Here’s some nice advice on building inexpensive cardboard hills.
Here’s some good advice on quickly building a relatively inexpensive wargames table.
Ironhands has a page with tips for creating sufficiently alien Eldar terrain for your Warhammer 40K games.
Given all of the Zombie gaming going on these days, there’s bound to be a demand for models of wrecked cars. Terragenesis has an article on making casts of car wreckage in plaster.