[Update: Check the comments for even better alternatives from @jasonkarns and @aaronjensen]
For the purposes of this I’m using https://github.com/defunkt/resque.
> git clone git://github.com/defunkt/resque.git
> git remote add plastic git://github.com/plastictrophy/resque.git
> git fetch plastic
> git diff origin/master plastic/master
Comparing branches the same way, just remove the repository reference. For instance,
git diff master myfeature