systemd is a technique and service manager for Linux, compatible with SysV and LSB init scripts.

systemd provides aggressive parallelization capabilities, makes use of socket and D-Bus activation for starting services, offers on-starting of daemons, keeps track of processes using Linux cgroups, supports snapshotting and restoring of the system state, maintains mount and automount points and implements an elaborate transactional dependency-based service control logic. It can work as a drop-in replacefor sysvinit.

Install systemd:

apt-get update && apt-get install systemd

Useful SystemD commands on Debian Squeeze:

List all running services :

systemctl

Start/stop or enable/disable services:

Start a  service:

systemctl start service_name

Stop a  service:

systemctl stop service_name

Restarts a service:

systemctl restart service_name

Show status of a service:

systemctl status service_name

Enable a service to be started on startup:

systemctl enable service_name

Disables a service to not start on startup:

systemctl disable service_name

Powering off the machine:

poweroff

Some other  possibilities :

halt -p

init 0

shutdown -P now

Enjoy.