For landscaping there are a ton of options now. Yes, you can still use the wire and mache direction, however with all of the different types of foams out there alot of scenery is done with insulation foam. It's lightweight, strong, can easily be carved and shaped, and is paintable right from the start.
GeoHex is a company that makes landscaping sections for tabletop miniature gaming. All of the bases for their pieces are done with the insulation foam.
Then you'll need to visit a model train or hobby shop that carries items from a company call Woodland Scenics. they have a HUGE selection of materials for making realistic terrain for whatever you need it for. There are other brands of terrain manufacturers but Woodland has the largest selection.
Foam is the way to go now adays. I work for a model
railroad manufacturer as a kit designer and we use
the pink 2" (or 1") insulation foam available at most
home centers (Home Depot or Lowes).
Woodland scenics makes most of the products you would
need to a landscape layout. I also found that using
dried floral and doing some light airbrushing gives you
more realistic looking trees and brush that the items that
they carry. For me, Trees and shrubs are the toughest
things to get to look real.
I guess it all depends on what you are planning on modeling.
Hope that helps you some.
Try this site. Lots of good info. on making your own plants trees and so forth. They even have a tutorial on making your set modular so it is easily expandable.
Been playing DND with my kids and we're starting to use miniatures. We used foam board to build a keep and it came out pretty good.
1 inch measuring 5 feet the keep is 10 feet high 100 feet wide 100 feet deep and has an additional 20 feet around the keep for terrian. Everything is built onto the foam board and it VERY sturdy.
Foam board can be bought at office max/depot and makes a good base for landscaping as well.