- Natural Earth Shapefile downloads for cultural and physical data sets for the entire earth.
- US Census Shapefiles and KML files for US shapes.
- GeoCommons Esri community site that makes it easy to share geodata. Reliability may vary!
- GeoNames Contains over 10 million geographical names. Free to use and download.
- Wikimedia Commons Tons of maps in SVG format. Easy to edit and customize for yourself.
- GetLatLon As simple as it gets. Search for an address, drag the map. Get a latitude/longitude point.
- Ogre - ogr2ogr web client Hand it a SHP, get back some GeoJSON. Hand it some GeoJSON, get back a SHP.
- Geo for Google Docs Google Apps Script for doing geocoding within a Google Spreadsheet. Very handy!
- Mapshaper Simplify a SHP in your browser. Will crumble on very large files.
- geojson.io Edit or create a GeoJSON file on the fly.
- epsg.io Plug in a location, get back a coordinate system.
- geocod.io $ Cheap bulk geocoding. First 2,500 per day are free.
- Landline + Stateline Landline is a JavaScript library that creates SVG maps from GeoJSON. It comes with Stateline, which makes creating responsive U.S. state and county maps easy.
- csvkit Powerful tool written in Python that let's you manipulate JSON and CSV data.
- OpenRefine
Make programmatic changes to datasets.
- Geocoding Hook it up to a geocoding endpoint and do mass geocodings!
- GDAL
You probably know about GDAL.
- ogr2ogr Everyone's favorite ogre dating service. Command line interface for data conversions and joining.
- Shapely Manipulate and analyze geometric objects in Python.
- Fiona API written in Python for OGR methods.
- Rasterio Clean and fast and geospatial raster I/O for Python programmers.
- QGIS Don't wanna pay for ArcGIS, but want similar functionality? Here you go.
- TopoJSON An extension to GeoJSON written by Mike Bostock (of d3 fame) that encodes topology, and make crazy small text representations of geodata.
- datamaps A tool for indexing large lists of geographic points or lines and dynamically generating map tiles from the index for display. (I know nothing about it.)
- Color Oracle Don't forget to account for color blindness!
- ColorBrewer 2.0 Trustworthy color palettes.
- Google Geocoding API $ Many caveats with Google's service. Probably will need to pay. Definitely has to be on a Google Map, or you break the TOS.
- Yahoo! BOSS Geo Services $ Doesn't have to use Yahoo! Maps (thankfully), but does require payment.
- Mapquest Open Geocoding API Based on Nominatim. Definitely the weakest, but also the free-est. Make sure to double check the results!
- Mapbox Geocoding Mapbox's in-house geocoding tool. They'd like you to ask permission before using it!