OSRIC (Old School Reference & Index Compilation) offers a free fantasy role playing game inspired by first edition Dungeons and Dragons. It’s not the first effort I’ve seen trying to recapture the magic of 1st edition, before the life was sucked out of it with the bloated later editions.
Dungeoneering dot Net has a nice selection of printable terrain tiles ostensibly for use with the Dungeons and Dragons miniatures game, but which would also work with any number of dungeon crawl games — of which there are many free ones available on this site.
The Last Alliance has an article on making Mallorn Trees — those huge trees amongst which the elves live in The Lord of The Rings. The idea is that the trees are so large — and their branches so high that only the trunks come into play in a game.
Now, I don’t have much use for Mallorn Trees, but it occurs to me that the same technique also could be used to make the trunks of trees in, say, the Brazilian rain forest. You could use some of those Copplestone pygmies and Amazon explorers.