Standard LAMP server for my environment monitoring, shared Calendar (davical, sync'd to Android gadgets, desktops, etc), data storage, web applications, email (getmail, postfix, dovecot, roundcube), etc.
Backup server (in another room from the first server), switched on by WoL each day, slurps data from server with rsync w/archival backup, waits a few minutes then shuts down.
10/100/1000 Mbps switch
802.11n Access Point
That's about it from the top of my head. The server is over 12 years old and still going strong. And it draws about 50 watts. The backup server is a much more modern machine, but its power draw is negligible since it's only on for about 20 minutes per day.