I have started using Git over Subversion. Following is the list of my git configurations.

Globally ignore .DS/_Store

echo ".DS_Store" >> ~/.gitignore
git config --global core.excludesfile ~/.gitignore

Information about me and my email goes here.

git config --global user.name "My name"
git config --global user.email me@olemiss.edu

I love colors

git config --global color.branch auto
git config --global color.diff auto
git config --global color.interactive auto
git config --global color.status auto

And I love TextMate

git config --global core.editor "mate -w"