RSpec documentation...where is it hiding?

Not sure why you feel rdoc.info isn't useful - here's the matcher docs there:

http://rubydoc.info/gems/rspec-expectations/2.0.1/RSpec/Matchers

It may be that you're looking in the wrong spot; these were in the RSpec::Expectations gem, which is split out from the core in Rspec 2.

The first place to go is the official Relish docs, they have gotten a significant improvement over the years and are now my first place to look.

At the time of writing this answer originally, this gist was solid. It contains matchers for the following:

• Capybara
• Paperclip with Shoulda
• Rspec Rails
• Rspec Exceptions
• Shoulda Matchers