i3lock is a simple screen locker like slock. After starting it, you will see a white screen (you can configure the color/an image). You can return to your screen by entering your password.
i3lock forks, so you can combine it with an alias to suspend to RAM (run i3lock && echo mem > /sys/power/state to get a locked screen after waking up your computer from suspend to RAM)
You can specify either a background color or a PNG image which will be displayed while your screen is locked.
You can specify whether i3lock should bell upon a wrong password.
i3lock uses PAM and therefore is compatible with LDAP etc.