I don't have a service in my run level that starts the login prompt, so I was wondering what does.
By 'login shell' you mean the login prompt you get when you hook your server up to a keyboard and monitor? And the same login shells on the other virtual terminals accessed with CtrlAltF2 and so on?
On RHEL 4 and 5, they are started in
On RHEL 6, they are started in
Edit: init is the first process started by our OS, it is what spawns all of your services. It has a PID of 1. When it starts it reads /etc/inittab and if you look at the lines that say reference rc with some number, that is what is starting your services at your desired run level. It likewise makes sure mingetty is running at your desired levels on your desired devices. You can read more on the the init section of wikipedia's article on how linux boots and this article on from power to bash.