One of my favorite sources of data is the city of Ann Arbor. The City of Ann Arbor Data Catalog holds many useful data sources for both GIS and numeric data. Many of files are downloadable in SHP and KML files for easy GIS use. There are also PDFs and Excel documents of other datasets. Two of my favorite datasets in this group are the Purchase Card transactions back to 2009 (which leads to all sorts of questions and interesting little vinettes of information about a municipality spends money) as well as the Ann Arbor Tree Survey, which is a GIS map of every tree owned by the city of Ann Arbor. The arbor, as it were, of Ann Arbor.