labs.google.com is the location of Google’s technology playground.
The site contains some of googles latest developments including the new 26 March Google Compute where you can donate your idle computer time into scientific research (similar to the seti at home, among others).
The Google Labs also contain some other interesting search software in development like, Google Webquotes, Google Sets, Google Glossary, Voice Search, Google Viewer, and Keyboard Shortcuts where you can navigate search results without using the mouse.
Update (2011): Google has retired Google Labs – Press Release