Seen on a git 1.6.0.4 installation (dunno about previous versions), installed through MacPorts ¹ with the +bash_completion option.

$ git config #tab
apply.whitespace               core.compression        ...
branch.                        core.fileMode           
clean.requireForce             core.gitProxy           
color.branch                   core.ignoreStat         
color.branch.current           core.logAllRefUpdates   
...

With sub-options too, on words ending with a dot:

$ git config remote.origin. #tab
remote.origin.fetch               remote.origin.receivepack      ...
remote.origin.push                remote.origin.skipDefaultUpdate

And as usual, calling git-config with a setting name without specifying a new value displays the current value.

$ git config remote.origin.url
git://github.com/evanphx/rubinius.git

Git’s getting easier by the day. Awesome!

1. A recent change from a previous position!