Tectonicus generates highly details maps of Minecraft worlds, and lets you explore them via google maps, with panning and zooming. You can then upload the generated map to the web and let other people looks around your map.
Download latest version (right click and select 'save as...')
For more information on running Tectonicus, see the page on the minecraft wiki.
For feature requests and feedback, please use the 'leave feedback' option to the left, or go straight to the feedback page.
You can also join the discussion thread on the minecraft forum.
Tectonicus is completely free, but if you like it then please consider donating to charity in it's name. There's a donations page. People who donate get a 'supporter' icon next to their player on all maps.