To see an old version of something:
    git show HEAD~1:path/to/file
Here ~1 means "1 revision before HEAD"


To find the commit in which you removed an object:
    git log -n 1 -- <filename>
To get it back:
    git checkout <commit>^ <filename>


To see everything on a remote repository:
    git remote show origin

To enable access to new remote branches, you might have to do this:
    git fetch origin

To create a local branch based on a remote branch:
    git checkout -b <branch> origin/<branch>
http://stackoverflow.com/questions/1783405/git-checkout-remote-branch

To erase the last commit without altering your index or checkout:
    git reset --soft HEAD~1

To reset your checkout to origin:
    git fetch origin && git reset --hard origin/master

To set a local branch to track a remote branch:
    git branch --set-upstream foo origin/foo

To run git with a different ssh key:
    ssh-agent bash -c 'git add <private-key>; git <cmd>'