Raildock is a free website that has a searchable listing of the Ruby on Rails documentation. The search bar even features AJAX’d autocomplete via a dropdown box.
It is a useful site and lets developers to find what they are looking for quickly and easily. I tend to have at least one tab open to it while I develop.
(I have heard reports that the AJAX does not fully work in some browsers. It works in FireFox 1.0 on both OSX and Win32 that I know of. It also takes a bit to load up so be patient)
Eric Davis