The Colonial Wargaming blog has a discussion and photos of various forms of tabletop hills and mountains, from the “rugged” to the “stepped” to the classic General Tremorden Rederring style profile mountains.
Dark Future Games has an illustrated article on sculpting chains from Green Stuff Epoxy.
Itty Bitty Battlefields has a post on making 15mm trench systems on the cheap.
The Wargame Terrain blog has a nice tutorial on making a thatched hut native village.
Here’s a nice tutorial on making insulation board hills for your wargaming table.