One vote for rubymine. It handles all the rubyisms like rvm, rbenv, bundler and the various servers nicely as well as syntax hightlighting for all the ususals plus haml, coffeescript etc.

It also looks like it will be getting nice Torquebox integration soon if you are a jruby / Torquebox person.

I must admit though that I do not use the advanced features half as much as I should.