Programming Ruby / The Pragmatic Programmer's Guide / Interactive Ruby Shell http://www.rubycentral.com/pickaxe/irb.html
interactive editor in irb (vim, etc.) https://github.com/jberkel/interactive_editor
The Tiger's Vest (with a Basic Introduction to Irb) http://mislav.uniqpath.com/poignant-guide/book/expansion-pak-1.html
irbtools is a meta gem that installs a bunch of useful irb gems and configures them for you. https://github.com/janlelis/irbtools http://rbjl.net/40-irbtools-release-the-power-of-irb