There are many very interesting Google APIs and time by time i find a new one accidentally (i.e. Google Geo Code API, or Google Elevation API).
Where do i find a complete list of all Google APIs? I haven't found any.
EDIT 2013/Sep/13: The links below seem outdated as they do not show a complete list anymore. I found another list at https://developers.google.com/apis-explorer/#p/ containing interesting things - but this one does not seem to be complete as well.
Any updated link is appreciated.
This link shows http://code.google.com/more/
Google Libraries API - Developer's Guide
The Google Libraries API is a content distribution network and loading architecture for the most popular, open-source JavaScript libraries. Using the google.load() method gives your application high speed and global access to a growing list of the most popular, open-source JavaScript libraries. You can also use tags to include the libraries.