Design docs here:

Source Map v3

Design docs for deprecated versions:

Source Map v2

Source Map v1

Implementation here:

com.google.debugging.sourcemap

Mozilla's JS Implementation here:

https://github.com/mozilla/source-map

Webkit JS Implementation here:

http://trac.webkit.org/browser/trunk/Source/WebInspectorUI/UserInterface/Models/SourceMap.js#L158

Blink JS Implementation here:

https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit/Source/devtools/front_end/sdk/SourceMap.js&type=cs&l=282

Discussions:

dev-js-sourcemap@lists.mozilla.org

Chrome's support of Source Maps discussed:

http://www.html5rocks.com/en/tutorials/developertools/sourcemaps/

A SourceMap encoding/decoding debugger: http://murzwin.com/base64vlq.html