Card bases - By Digger

If you are looking for lots of card bases for your projects, take a trip to your local motor registry (RTA in NSW-Australia) and pick up a handful of cardboard learner plates, they are free and make ideal bases for rocks and trees.

Where to get sand - By Cliff

You can good cheap good consistency sand from pet shops. I think I bought 500g of fine white sand for $2-$3. Very clean and great for terrain.

Foam board - By Cliff

5mm foam board (foam with cardboard on top and bottom) is available from OfficeWorks. Comes in 1 or 3 sheets of 50cm by 60cm. 3 sheets for ~$30. I use it for movement trays (cuts very easily with a craft knife) also possible to use for sides of buildings or other projects.
I brush foam with PVA glue prior to spraying - no problem.

Cutting Styrofoam - By Leondus

The Wonder Cutter.
Under $9. Contains a wire heated by two D-Cell batteries with four replacement wires.
It does burn D-Cells really fast, I used mine at first non-stop for three hours before replacing the cells.
Michaels arts and crafts (I paid $7.95 for mine there)

Dremel 1550 VersaTip Tool Kit - Wal-Mart
for cutting foam, it come with a attachment which is a "x-acto" knife blade. Can be found in the Arts & Crafts section

You don't have a wire or blade cutter handy?
Use an electric carving knife or another knife with a sharp blade. Smear some soap as lubrication on the
blade helps.