This'll be a recurring series into 2013 and I'd like to first introduce Better Errors, which incidentally can be used outside of Rails as it simply hooks into the middleware of Rack apps.
Simply
group :development do
gem "better_errors"
gem "binding_of_caller"
end
I've included the binding_of_caller
gem to allow using Better Errors' advanced features (REPL, local/instance variable inspection, pretty stack frame names) although, this is optional.
Next up, is RailsPanel and this is described by most quite simply as 'Wow'. It's a Chrome extension and gives the Chrome inspector insights into your Rails app... oooh!