Using bloated desktop managers such as KDE or even Gnome isn't really into my blood, therefore one of the many separate applications I must install when setting up a decently comfortable environment enabling multi user sessions is a login manager. Since KDM and GDM are not an option, XDM or SLiM could be a reasonable choice among the lightweight display managers.
Though I've successfully used both XDM and SLiM in the past Qingy is my current favorite application for this task. Here's a short description from Qingy's website: "qingy is a replacement for getty. Written in C, it uses DirectFB to provide a fast, nice GUI without the overhead of the X Windows System. It allows the user to log in and start the session of his choice (text console, gnome, kde, wmaker, ...)." As you can see typical login managers rely on X, even the most lightweight ones whereas Qingy needs nothing more than the framebuffer device driver saving considerable amounts of memory and processing time. This gains come at no extra cost, Qingy is eye candy enough with all sort of goodies like icons for suspending, rebooting or shutting down and a fully themeable interface.
Moreover since it doesn't actually start X it allows the user to login either to an X session or simply to the console, something I find particularly useful when I boot my desktop just to perform some command line tasks. Setting up Qingy is quite straightforward, /etc/qingy/settings provides nice defaults and every single option is well documented. Qingy's motto says it is a replacement for getty, so you must also edit /etc/inittab and replace some respawn actions. In my case I like to have two Qingy instances running on the first two virtual consoles and keep agetty (the alternative Linux getty that comes with Arch Linux) running in the remaining ttys:
c1:2345:respawn:/sbin/qingy tty1 c2:2345:respawn:/sbin/qingy tty2 c3:2345:respawn:/sbin/agetty -8 38400 vc/3 linux c4:2345:respawn:/sbin/agetty -8 38400 vc/4 linux c5:2345:respawn:/sbin/agetty -8 38400 vc/5 linux c6:2345:respawn:/sbin/agetty -8 38400 vc/6 linux