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.
For instance, someone asked if front-rounded vowels (e.g. German /ü,ö/ or French /œ/) were only found in languages originating from northern Eurasia. The map at http://wals.info/feature/11 actually shows that while most languages with front round vowels are in Northern Eurasia, there are a few further south in tropical regions including a few in the Amazon basin. In case you’re wondering the maps are in the Google maps format and can be exported into KML and XML format.
The sources are well cited so the data is trustworthy and lots of features are mapped out. There’s also a subsidiary set of language profile pages. A nice academically rich use of Web 2.0 technlogy.