Komodo Edit is free and works pretty well. It needs more than a
minimal configuration to run okay. On the Mac, a lot of people like
Textmate. I find the 'e' texteditor just fine for a windows laptop --
it's cheap but it's not free. Komodo Edit pauses and goes to sleep
(or garbage collects) on my half-gig laptop, I simply ran out of
patience. Both 'e' and Komodo edit do just fine with Ruby and Rails.
Komodo has more features. The full Komodo IDE is expensive, so I've
The Aptana IDE is free but is a tremendous resource hog compared to
the others. It has good functionality but goes to sleep for extended
periods. Some people blame the Java/Eclipse underpinnings of Aptana
for it's lack of responsiveness.
If your a really good emacs hacker you can make emacs do what you want
but it seemed it was taking forever to configure and then it didn't
work right for me. Last time I looked there are about three or four
different packages you have to integrate into emacs to get it play as
nice as the others.
I hear good things about vim. I've heard that NetBeans is good but a
Visual Slickedit has a fantastic feature set but is definitely not
free and not oriented toward Ruby and Rails, the last time I looked.