Four drawers I have fostered through my years in Powercore:
Managed Services - actively monitoring individual computers, networks, email, and communications to stay ahead of problems.
Installations - wired and wirless networks, cabling, new computers, new phones, or other new technology.
Backup - Backing up important data, but also checking the backups to confirm good function.
Security - Antivirus, white labeling, firewalls, and support for users
My favorite service is setting up a new office space. When I have the opportunity to set everything up from the beginning, everything is clean, fast, and documented.