[maxerickson]

OpenStreetMap would be fine as the base map there. There's nice clean tiles available from several providers.

And while I am not experienced with them, I believe both Leaflet and OpenLayers would work well to build the interactive part of the map.

[everybodyknows]

Example of a data set visualized with Leaflet by a US Federal agency:

https://earthquake.usgs.gov/earthquakes/map/

Suffers from a few scaling pains.