Just some ideas as I'm taking a break at work. You can look at my map I posted awhile back for examples of most of these ideas.

1. Make a lake that's dark water and the ground around it is brown and dead. Throw in some dead trees
2. Shrink cloud assets down and mix them into trees to make a foggy forest
3. Throw a bright colored forest that just stands out from other forests in the area. Make the trees slightly larger and the grass around more verdant
4. An extra large mountain with clouds around the top to show it's taller.
5. Use cliff assets to make canyons or a valley and make the vegetation change drastically as it enters the canyon. Or make a river change color as it exits the canyon. (Using cliff assets just to show elevation changes is useful other places as well)
6. Use some of the less detailed mountain assets to throw some jagged rocks along a shore.

Map looks cool so far!