Download:
GeoGebra download
GeoGebraTube - the great new resource for finding sketches and uploading and sharing your work. Wonderful.
Java (on the off chance that you need an update. PC only. Mac, use Apple Software Update - unlikely it's needed.)
GeoGebra Prime a version of GeoGebra for elementary school
Some samples of GeoGebra for mobile devices. (Use HTML5 instead of Java.)
GeoGebra 3-D in development (if you just can not get enough GGB)
GeoGebra 4.2 Beta has an export to HTML 5 feature that helps with mobile. (Also has Computer Algebra System in development.) Link goes directly to download. Release Notes.
Reference
GeoGebra Wiki (lots of GeoGebra resources)
GeoGebra online help
GeoGebra Forums
Guillermo's Links
Mike May's 4.0
Guide to Computer Algebra System commands.
Very different: kind of a GeoGebra top news site.
Tutorials:
Guillermo Bautista's GeoGebra series.
Nordin Zuber's GeoGebra HowTo
Bowman Dickson's GeoGebra for the Classroom tutorials and links
Mike May's excellent GGB 4.0 Workshop
Richard Wade's nice intro tutorial: Intro GeoGebra
Dave Matthew's GeoGebra Page
Marc Renault's Tutorials
University of Limerick Workshops
Content
The Wiki listed in reference.
Linda Fahlberg's Geogebra Wiki (for teachers) and her older GeoGebra Resources.
John Golden's GeoGebra page; topics from elementary through university. Includes a link to some of my favorite GeoGebraTbe authors.
Brevard School's GeoGebra page
Marc Renault's GeoGebra samples
Broken Airplane's GeoGebra resources
Nick Bennett's math wiki; more of a focus on teaching the students to use GeoGebra than complex sketches.
Example of livebinders for embedding GeoGebra.
2011 GeoGebra Midwest Conference
Common Core State Standards: Math
Connections
A Twitter list of some expert GeoGebra users
North American GeoGebra Journal
GeoGebra on Facebook
Grand Valley GeoGebra group on Facebook