IntelliJ 8.0 was released yesterday and after installing the Ruby + Rails plugin, IntelliJ is very competitive with the NetBeans for Rails development.
One feature that I particularly like is the jump links in the editor that let you jump from a controller method to the corresponding view template. There are also links from a method to the super class method that is being overridden (if any). There is currently a small bug in the plugin: multiple identical jump links are shown; all work the same.
In some ways it is nice to have Java and Ruby support in one IDE, but there are "Java only" menus shown while working on Rails projects - that is one advantage of the new RubyMine IDE: basically IntelliJ with all Java support removed. At the current time, Rails support for IntelliJ 8.0 seems to be more stable than the prerelease version of RubyMine but it will be interesting to compare the two next year when RubyMine is released as a product.