The Wargaming Depot blog has a tutorial on making terrain tiles from cork.
It’s an idea that I considered for quite some time, before finally settling on doing a similar thing with 1 foot square carpet tiles.
Modeling
Hills, Mountains and Cliffs For Wargaming
The Schild en Vriend site has a nice article discussing hills, mountains and cliffs on the wargames tabletop
Casting Bunkers In Plaster
Terragenesis has a nice article on casting bunkers in plaster from chocolate boxes.
Building Mad Scientist Labs
Terragenesis has an article on building laboratory equipment for mad scientists. The photos show an amazing use of various household and electronics bits.