Good stuff, I can see a certain style there.
If you want some more tools (free), check these out
Project Dogwaffle - good paint program, has a lot more tools to it than Paint
the Gimp - a free 'photoshop-like' program that allows you to layer scenes, use filters (cartoon effects, black and white, borders, edges, etc).
Wings 3d - ok, this is a stretch, but you can make 3d models of things and import them into other programs.
Also, check out a place called Daz 3d (if you want to use 3d people in pictures) for Daz Studio.
Terragen (planetside- site), and Bryce 5 - there are free versions out there. They both do landscapes, although you can put in foliage in Bryce.
Ok, I'll stop. 3d art is what I try to do. My avatar was made with Bryce, WIngs, and Poser (which is not free, unfortunately, but does the same thing as Daz Studio).