You can install Noobs, install Raspbian via Noobs and then use the retropie setup script to install retropie.
You cannot install anything along Noobs but you can use Noobs to install multiple operating systems, i.e. raspbian and openelec. Alternatively you can use Berryboot to do the same thing (install multiple os). Berryboot additionally has a prepared retropie image and someone here in the forum created a new Berryboot image for Retropie 2.6.