One of my favorite features of Ruby is Ruby Gems, the powerful package manager. There are tons of Ruby libraries available as gems such as Rails, Mongrel, and even one for Twitter. The gem I find the most useful nowadays is called cheat. Cheat basically puts tons of cheat sheets inside of your command line, so that you have quick access to the information you need without resorting to those hard to read man pages.
sudo gem install cheat
Cheat is made available by the guys over at Err free, the geniuses behind both FamSpam and GitHub.