There are a number of options. Most Rails developers seem to prefer lighterweight options like TextMate. There's also a great Rails.vim plugin if you're a Vi sorta guy.
If you're looking for a more heavyweight traditional IDE, I can heartily recommend NetBeans, which has evolved to have phenomenal Ruby/Rails support. Other options include Aptana/RadRails (Eclipse-based), IntelliJ, and Komodo.
Joined: Sep 01, 2008
Btw, NetBeans is available free of cost. I'd start there if you're looking for a traditional IDE. Rails.vim is also free, of course.
Joined: Jun 18, 2007
GVim with Ruby support and Rails.vim is awesome. (There's a reason why Timothy Pope, author of Rails.vim, is in the acknowledgments for my book.)
Take it easy,
Joined: Jul 02, 2001
Thanks Nick and David!
Being an Eclipse guy I think I'm going to try Aptana Rad Rails first.
I don't have the luxury of playing around with a new IDE (at least for now).