I generally use the Wingdings, also. Also, Photoshop and Illustrator shapes sometimes see some use. If I need a particular special symbol, like the alchemical symbols for the mines on my Tawaren map or the various icons on my Wheel of Time map, I make those by myself. If I decide I want to use isometric icons, I'll probably dig into the symbol libraries that came with CC3 or make them myself.

The only real rule in using symbols (other than to make sure they're free of copyright encumbrances) is to be consistent and either include a legend or make it very obvious what each symbol means.