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.
terrain
Build A Cheap and Quick Wargames Table
Here’s some good advice on quickly building a relatively inexpensive wargames table.
Making Eldar Terrain For Warhammer 40K
Ironhands has a page with tips for creating sufficiently alien Eldar terrain for your Warhammer 40K games.
Wrecked Cars In Plaster
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.