This deal has expired!
This one is pretty cool! A few days ago, Google rolled out a new feature for Gmail -- the ability to call US and Canadian phone numbers for free
. Voice chat has been available through Google Chat for some time, but the official ability to call phones directly is new. You'll need to install the Google voice and video chat plugin. After that, you should be able to use the "Call phone" option under "Chat" inside Gmail. Technology news outlets have reported that the free calling between the US and Canada is good until the end of the year. After that, Google hopes that international calling fees will keep the serivce between Canada and the US free.
Google didn't make the "Call phone" option immediately available to all Gmail accounts, but they have been rolling it out steadily since August 25. If you don't see it yet, it should appear soon.