A few resources have been particularly helpful for me as I have started to use openSCAD.
The main openSCAD site: http://www.openscad.org/
The openSCAD site describes the program, and the scripting approach it takes to 3d modeling. Installation files are available for Linux, Mac OS X, and Windows. The site also links to a number of other openSCAD resources, some of which are described here.
The openSCAD user manual: http://en.wikibooks.org/wiki/OpenSCAD_User_Manual
The manual is very helpful in learning openSCAD. It is concise, and easy to read. I have used the language documentation section extensively, especially as I try to complete more complex models.
EduTech Wiki openSCAD Beginner’s Tutorial: http://edutechwiki.unige.ch/en/OpenScad_beginners_tutorial
This tutorial is a good companion to the openSCAD user manual. It covers a lot of the material in the openSCAD language documentation, but some of the examples are easier to understand than the examples in the manual.
Thingiverse Blog posts: http://blog.thingiverse.com/2010/12/10/getting-started-with-openscad/
Thingiverse is a site that allows people to share their digital designs, and to share their approaches to 3d modeling. It focuses on the physical printing process as well as the design process. The authors of the site are fans of openSCAD, and they have a number of posts about using openSCAD on the Thingiverse Blog. The topics range from the very simple, such as using openSCAD for the first time, to more complex topics such as for loops and bezier surfaces. There is also a small series of tutorials on the site.
I Heart Robotics blog posts: http://www.iheartrobotics.com/2011/02/openscad-tip-round-1-of-3.html
The I Heart Robotics blog has a number of posts about more advanced uses of openSCAD. For example, there are posts about making rounded edges and corners, and making helical and toroidal shapes.
The openSCAD Mailing List: http://rocklinux.net/mailman/listinfo/openscad
There is a mailing list available for people interested enough to join, or to browse the archives. It is more focused on the development of openSCAD, but if you have a question about using openSCAD that does not seem to be answered elsewhere, it might be worth a visit to the archives. Marius Kintel, the creator of openSCAD, is actively involved in the list.
Next: Your First openSCAD Model