I’ve just uploaded a new plugin to WordPress. GeoJSON Maps facilitates displaying multiple GeoJSON feeds on a map. It has a custom legend to toggle on/off each data layer. The map can be displayed on a WordPress post or page via a short code. All you need is some GeoJSON feeds (both json and jsonp) and some styling markup. See here for a demo.
This plugin is a result of work we have been doing with the NYC Dept. of Transportation. It allows city administration to easily publish data on a map in a WordPress blog without the need of any custom programming. Here is an an example of where this type of map is used, in showing the results of a study of the Jackson Heights neighborhood.