Here are links to tools and API libraries and documentation that were posted in the group. Please let me know if I forgot something. 

Tutorials and other documentation:

 - http://code.google.com/apis/chart/

 - http://pmougin.wordpress.com/2007/12/10/google-chart-api-fun-with-cocoa-and-f-script/

 - http://24ways.org/2007/tracking-christmas-cheer-with-google-charts

 - http://themechanism.com/blog/2008/03/30/thematic-mapping-with-the-google-charts-api-a-brief-tutorial/

 - http://www.programmableweb.com/api/google-chart/mashups

Chinese translation of the documentation: 

 - http://labs.cloudream.name/google/chart/api.html

 - http://labs.cloudream.name/google/chart/faq.html

Tools to create charts: 

 - http://www.style.org/chartapi/

 - http://tkhere.googlepages.com/tkgooglecharter.html

 - http://charts.hohli.com

 - http://www.tagarga.com/files/gcui

 - http://jonwinstanley.com/charts/

 - http://chartpart.com/  

 - http://www.acme.com/chartmaker/

Tools to plot  functions:

 - http://www.felipebarone.com/plot-function-google.php

Java:

 - http://code.google.com/p/gchartjava/

 - http://code.google.com/p/javagooglechart/ 

Ruby:

 - http://rubyforge.org/projects/gchart

 - http://code.google.com/p/gchartrb

 - http://code.google.com/p/google-charts-on-rails/ 

 - http://douglasfshearer.com/blog/ruby-google-charts-api-data-encoding 

C#   / .NET

 - http://code.google.com/p/ngchart/ 

 - http://code.google.com/p/googlechartsharp/

 - http://groups.google.com/group/google-chart-api/browse_thread/thread/e919d78675685b7d 

Python: 

 - http://code.google.com/p/google-chartwrapper/

 - http://pygooglechart.slowchop.com/ 

ABAP: 

 - http://code.google.com/p/abapchart/ 

PHP: 

 - http://code.google.com/p/gchartphp/ 

 - http://www.style.org/chartapi/code/ 

 - http://www.malaiac.com/GphpChart

 - http://www.phpclasses.org/browse/package/4299.html 

Perl:

 - http://search.cpan.org/~marcel/Google-Chart-0.02/lib/Google/Chart.pm

Wiki integration

- http://code.google.com/p/gchart4mw  

Grails:

 - http://grails.org/Google+Chart+Plugin