This has been requested quite a few times (including here and here) and is a widely used approach to visually condense large numbers of Markers.
TheĀ Leaflet.markercluster plugin (demo here) could be a potential solution for this, however by default the clusters obscure the appearance of the underlying Markers:

While I think this implementation would be a good solution for some users, I would like to offer clustering that displays the Marker Types contained within each cluster.
I put together a crude prototype to illustrate this. Without clustering:

With clustering:
