MapBox http://geojson.io/

MapBox http://geojson.io/ 

A very nice map where you can overlay your own  GeoJSON, TopoJSON, KML, CSV, or GPX files by simply dragging and dropping into the drop zone

Very clean and straight forward map interface.

Also available is a simple editor for creating your own graphical shapes. 

Give it a try:

http://geojson.io/