Hi,
in my feedreader I found a link to interesting gem - better_errors (https://github.com/charliesome/better_errors).
It makes rails (and not only rails) error page in development env more usable than before. It makes stacktrace clickable and for each line in stacktrace it displays source code around that line, list of local and instance variables with values and interactive REPL inside that error page.
Hope it will make development of ruby/rails apps easier.
-- Petr Blaho, pblaho@redhat.com Software Engineer, CloudForms