Dynmap

Dynmap is a plugin which automatically creates live-updating maps of Minecraft worlds which are publicly viewable in browsers.

The Spinalcraft network has two worlds, Ascension and Legacy; the maps of both are accessible online. The map for the most recent Ascension world is available at ascension.spinalcraft.com, and the map for the older Legacy world is located at legacy.spinalcraft.com.

You can zoom in, out, and scroll around the map to look for biomes or other points of interest. It also has a menu to the right which allows you to switch between worlds (the Nether, the End, etc.) and locate other players.