Forgot to mention that railscasts.com has awesome screencasts on all kinds of topics. - Also, if you prefer to read them instead of watching, most are available on http://asciicasts.com/.

Also, a word of caution - http://guides.rubyonrails.org is currently based on rails 2.3. http://edgeguides.rubyonrails.org/ is probably the best place to look for the moment if you want to start with 3.0.

The edge guides actually follow the current master branch while the regular guides follow the current stable branch. Since 3.0 is kind of in limbo between the two (as an RC, it has it's own stable branch, but it hasn't been released yet), it's pretty much completely in sync with edge. Once it's released, everything should switch over to guides having info for 3.0 (the index page should list what version it's currently for).

...That was probably more than you ever wanted to know about Rails guides.