Xscreensaver with Xmonad

Install xscreensaver from the repository, then add the highlighted line to your .xinitrc file.  Make sure it is before the final call to xmonad in the .xinitrc

if [ -f $HOME/.xresources ]; then
xrdb -merge $HOME/.xresources
fi
if [ -f $HOME/.xmodmap ]; then
/usr/bin/xmodmap $HOME/.xmodmap
fi
xscreensaver -no-splash &
xmonad

This will launch the xscreensaver daemon when X is started.  To configure the user options run

$> xscreensaver-demo

To lock the screen from the command line run

$> xscreensaver-command -lock