lxdm

lxdm, short from Lightweight X11 Display Manager, is an open source graphical login manager originally designed as part of the LXDE (Lightweight X11 Desktop Environment) window manager.

These days, lxdm can be used as a standalone display manager for any other desktop environment, running on any Linux operating system that has a package for it in its default software repositories.

lxdm is pretty sleek, as it features support for user avatars, session switcher, language switcher, keyboard layout switcher, and a quit/restart button. It can also display the current date and time.