I kind of shamed myself into doing a bit more. Expect an update in a bit. I've working on a fog thing right now.

http://www.chaos.foxmage.com/tilesetx.png
The fog is meant to be transparent, perhaps moving. I'm not sure how well it came out. I suppose we'll see once someone tries compiling and testing.

Some other parts require more explanation. The thing under the rain is the thunder tile, for whatever thunder animation you need. Don't ask me why I made it minutely light blue/white striped.
The slightly off-black tiles are meant to be areas of darkness. You know how some tilesets have tiles for rays of light, to be made transparent and put in layer 3 for when you want a shaft of light entering a cave? I decided to experiment here and see if the opposite could be done- all of the cave except for the rays of light could be covered in transparent blackened tiles. If you think it won't work, you could just turn the things in to generic rays of light, I don't care.