The Google Classroom is a term coined by Google techies in 2009. It refers to the use of various google applications with students both inside and outside of the classroom.
Examples of Google Applications include:
Google Earth - http://earth.google.com/download-earth.html
Google Docs - http://www.google.com/google-d-s/b1.html
Google Sketch Up - http://www.google.com/sketchup/download/
Google Calendar - http://www.google.com/intl/en/googlecalendar/about.html
and
Blogger - https://www.blogger.com/start?pli=1
These are the most popular google applications to date, but it is the combination of the google applications that makes them more powerful as a learning tool.
Examples of other applications can be viewed at http://thegoogleclassroom.com/.

Google Labs have many apps that are very useful in your classroom and useful for you:

Quick Research Tools:
Public Data - http://www.google.com/publicdata/home - web2.0 graphic search engine
e.g. Population past and projections - China, India, Australia and Indonesia - http://www.google.com/publicdata/explore?ds=ltjib1m1uf3pf_&ctype=l&strail=false&nselm=h&met_y=evopop_t1&hl=en&dl=en#ctype=l&strail=false&nselm=h&met_y=evopop_t1&scale_y=lin&ind_y=false&rdim=country&idim=country:AUS:IND:CHN:IDN&hl=en&dl=enImage Swirl - http://image-swirl.googlelabs.com/ - image search engine
e.g. Science and Technology search - similar to wonderwheel but with images
http://image-swirl.googlelabs.com/html?q=science%20and%20technology#1

Google Squared - constructs a quick research grid - http://www.google.com/squared
e.g. Teaching Strategies - http://www.google.com/squared/search?q=teaching+strategiesGoogle Trends - http://www.google.com/trends - a comparative search engine investigating popularity
e.g. A search looking at Australian Curriculum and the QSA - http://www.google.com/trends?q=national+curriculum,+qsa&ctab=0&geo=au&geor=all&date=all&sort=0

Google Wonder wheel - http://www.googlewonderwheel.com/google-wonder-wheel-step-by-step
A spider map search engine to allows the user to find information in a different format

Posters for the classroom:
http://static.googleusercontent.com/external_content/untrusted_dlcp/www.google.com/en//librariancenter/downloads/Tips_Tricks_17x22.pdf