git rev-list --oneline master ^origin/master
Git rev-list will list commits in one branch that are not in another branch. It is a great tool when you're trying to figure out if code has been merged into a branch or not.
--onelineoption will display the title of each commit.
^operator excludes commits in the specified branch from the list.
git rev-list foo bar ^bazlists commits in foo and bar, but not baz.