Which IDE should I use with Ruby on Rails?

The answer depends on what sort of programming environment that you are used to using. If you are just learning a Rails then it's best that you don't burden yourself with learning a new IDE too. If you've already been using an IDE for another programming language, then I suggest sticking with the Rails equivalent, at least until you're familiar with Rails and its rake commands.

Some popular IDEs that have Rails support are:

Many developers who use Ruby on Rails prefer to develop using a text editor rather than an IDE. See: Which text editor should I use with Ruby on Rails?