RubyMine 3.0 has been released. RubyMine is a full-featured Ruby IDE from JetBrains. Release 3.0 has a huge range of improvements, and it's worth taking a look.
"But why should I use an IDE?" you may ask. After all, your trusty editor such as Vim or TextMate is just fine, right? However, if you haven't used a modern IDE like RubyMine, you might not even know what you're missing. It does a bit more than project management and file editing.
First, just take a look at the new feature list. It has things like integration with Git from the GUI, test coverage with RCov, a graphical debugger, RVM support, refactoring, and the list just goes on.
The only downsides to RubyMine that can be seen at first glance is the price ($69 for a personal license) and resource usage. Text editors use virtually no resources, and are very easy on the battery life. Big IDEs like RubyMine really do use a considerable amount of resources, and are not easy on your battery or CPU. But, on the bright side, RubyMine has a mode to cut resource usage when you're on battery, so they do help you out as much as they can.