Nice: RubyMine 2.0 will be a free upgrade
In a world filled with great free IDEs, JetBrains keeps being competitive with commercial IDE offerings.
I think that their RubyMine product is hands down the best Ruby development environment (although I do sometimes use GEdit on Linux and TextMate on OS X). Offering the 2.0 upgrade for free (to be released in a few weeks) is a nice way to say thanks to their customers. A beta 2.0 download is available here. I'm running the beta right now, and it looks like a good upgrade.