Links below provide some sources of geographic data as well as some tools for working with spatial data within R.

• For those coming to R with some spatial data background, this is a great explanation of coordinate reference systems with R syntax.
• General Transit Specification Feed (GTFS) Data for Metro Transit - St. Louis.
• Tutorials and documentation for using Leaflet in R and for the original leaflet.js javascript library.
• A list of choices of basemap styles, together with preview images helps you decide which tile server to use.
• St. Louis County data available for public download, including municipal boundaries.
• For a detailed presentation of how to make maps within ggplot using ggmap, see this vignette by Robin Lovelace.
• A description of many useful packages is available in the Spatial Task View on CRAN.
• Robin Lovelace et. al. - tutorial on visualizing spatial data in R
• Data, including shapefiles from the City of St. Louis
• Shapefile of National Park Boundaries.
• WashU Research Guide on GIS - links to data, software, maps, and more
• A guide to working with Census Data in R