[shajith]

One great starting point is ActiveSupport, specifically the core extensions:

http://github.com/rails/rails/tree/master/activesupport/lib/...

Though this library isn't really Rails-specific, it has a bunch of self-contained ruby files, good to learn about the style of doing things elsewhere in rails.

Examples: Array#uniq_by, String#pluralize, Numeric#hours, etc.

The Rails router, while considerably more complex than ActiveSupport, is also a self-contained chunk of code you can read: http://github.com/rails/rails/tree/master/actionpack/lib/act...

Also: When reading Rails code (or any ruby library's code, for that matter), I've found that reading the specs first is very effective.