With version 2.13 of Git and later, --recurse-submodules can be used instead of --recursive:
git clone --recurse-submodules -j8 git://github.com/foo/bar.git
Editor’s note: -j8 is an optional performance optimization that became available in version 2.8, and fetches up to 8 submodules at a time in parallel — see man git-clone.