The World Atlas of Language Structures Online (http://wals.info/feature) from the Max Planck Digital Library is a great new resource that maps languages with phonological, morphological or syntactic features.
I wrote it up in my linguistics blog If you’ve ever wondered which continents have tonal languages, go visit http://wals.info/feature/13.
I love that all the data sources are cited and that you can export map data as XML or KML (for other GIS programs) – I could recreate a version for myself if I wanted. My only recommendation is to shrink the size of the icons to 10.