Guides

The three main guides where I spend my time these days are available at the Autodesk website. To find the documentation page, you start in Revit. Click the help menu, then click tutorials. A window pops up explaining that all the tutorial information is available online at the Autodesk website and a link is provided. Clicking the link opens your browser to the documentation page.

It's nice that the actual Autodesk documentation can be so useful. When learning Architectural Desktop (AutoCAD Architecture) I relied almost exclusively on outside sources.

My big 3 are:
Revit Architecture 2009 Families Guide
Revit Architecture 2009 Imperial Tutorials
Revit Architecture 2009 User's Guide (basically your instruction manual but still useful)

Here's the current link to the Autodesk documentation page.