A JS Library For Interactive Maps – Leaflet
With a very easy-to-use API and OOP-based code, the library is modular and extensible.
It has support for features like drag panning, scroll wheel or double-click zoom, zooming animation, pure CSS3 pop-ups and more.
Leaflet is lightweight, very well-documented and supported with examples.
P.S. Although the examples on the resource page use only OpenStreetMap, other popular providers will work with the library as well.