There's a couple of great tutorials on this board - how to build a lava field board is superbly easy to follow and build and end up with something good. There's a few others that look great too...
Here's the lava board - thread is still active and I really can't stress how well it turns out, even for a novice.
http://www.dakkadakka.com/dakkaforum/posts/list/243963.page
This thread is a bit older but it's so gorgeous I almost want to cry every time I see it. Uses a lot of woodland scenics so it's probably a bit pricey to put together.
http://www.dakkadakka.com/dakkaforum/posts/list/216664.page#358954
Here's a nice Necron Tomb-World. I guess the guy that built it had access to a somewhat serious shop of tools, but I have it bookmarked for inspiration when I want to do something different.
http://www.warseer.com/forums/showthread.php?t=188236
Autumn Foothills - I have a LOAD of pine trees I picked up on clearance (Literally 100 or so of the Christmas Village trees - paid something like $3 for a package of 21 and bought maybe 6 packages) and was thinking of doing a mountainous terrain to showcase them - this board seems pretty close to what I want, just have to think on it a bit more before committing.
http://www.warseer.com/forums/showthread.php?t=113351
Here's a smaller piece for a temple of one sort or another. It looks easy enough to throw together and my buddy keeps pestering me to make some Chaos stuff because it's the faction I play.
http://www.warseer.com/forums/showthread.php?t=210283
The big two things you need to buy is foam and
MDF board (Arguably - Cardboard works but a sheet of
MDF lasts so long it's gross).
Everything else I use for terrain tends to be from trash/packaging/broken junk.
I'm working on a small space station now - I'll get some pics up once I'm a bit further along. Biggest holdup is waiting for glue to dry : /