RoR Charts

Google Chart Tools
http://code.google.com/intl/es-419/apis/chart/

http://badpopcorn.com/blog/2008/09/08/rails-google-charts-gchartrb/

Gruff Graphs for Ruby
http://nubyonrails.com/pages/gruff

Ref:

1 http://stackoverflow.com/questions/87561/what-is-your-preferred-way-to-produce-charts-in-a-ruby-on-rails-web-application