A number of git commands take the --name-only argument which can help give you an overview of what is going on between two branches, or in a specific commit.
$ git show --name-only <commit>
This will give you a list of affected files in commit
Alternatively if you don't care what differs in the specific contents between two branches, and only want to see different files you can do
$ git diff master..origin/master --name-only
This will show you the list of files that are different between your local master branch and the remote master branch. Handy if you have just done a git fetch and want to see what's different before merging or rebasing.