if you want to go for a satellite style map without symbols, then you can do it all in photoshop. If you want a symbol map, then for trees I would do a search for Ramah's 'Tree thing' which is a javascript program which will generate symbol forests for you against a png mask which you create. Takes about 20 mins to learn how to use if that. It comes with a standard set of trees.

For mountains and towns and suchlike, there are photoshop brush sets that you can download but you'll have to hunt for them in the mapping elements section (::edit :: oops, sorry Jax, I'm repeating you!)