"If RADRails doesn't capture your fancy and you'd rather use regular Eclipse as your Ruby IDE, Tabrez Iqbal has a great walkthrough of setting up Eclipse and using it to develop Ruby applications along with lots of screenshots and useful information."
(Via Ruby Inside.)
The eclipse IDE is amazing. I've used Aptana, which is based on eclipse and it certainly makes editing web applications a whole lot easier. Here is some more web application stuff eclipse might be able to do for you.