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://code.google.com/codesearch#OAMlx_jo-ck/src/third_party/WebKit/Source/WebCore/inspector/front-end/CompilerSourceMapping.js

Discussions:

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