Getting a list of unversioned files in a Git-controlled folder is way more annoying than it needs to be. Unless I really suck at reading man pages, it doesn't look like Git provides a facility to perform this operation on its own.
There may be a more elegant way of performing this, but here's a one-liner I threw together for this task, in case anyone else ever needs to use it.
Edit: turns out there's a standard way to do this that already works well.
git ls-files --other [--exclude-standard]
Or...
git clean -dnx | cut -c 14-
If you don't want to see ignored files,
git clean -dn | cut -c 14-