Because Bruce Eckel wishes Ruby had something like the Python Quick Reference. Because I find the framiness of the core and stdlib RDocs intolerable. Because I also have a hard time reading RDocs on account of their default colors.
I've created a Ruby API Guide. The Guide also includes a JRuby Cheat Sheet.
I finally splurged and bought a Ruby book: Ruby Cookbook, which I find both fascinating and helpful. Although it's almost a couple years out of date, it does a good job of presenting Ruby 1.9 and anticipating 2.0. The index, however, is not as thorough as I'd like. So, now and then I add to my own idea of a Ruby Cookbook index.
I hope you find these pages useful. :-)— Elizabeth Wiethoff