Cable locks are a simple way to increase any computer's security at very low cost. Almost all laptops have a special Kensington lock port, and most desktops have a metal loop that extends from the back and through which you can run a security cable. (Computers that don't have a lock port can instead use a "universal" lock system that attaches directly to the chassis.) Connect the computer to a desk with the cable, and you've added sufficient security to thwart most smash-and-grab operators. Be sure to store the keys to the cable locks in a secure location. You should also use a cable lock whenever you take a laptop out of the office.
LoJack for Laptops is software that runs unnoticed in the background but lets your laptop broadcast its location when you report it as lost. This helps law enforcement locate the computer more easily and enables you to wipe its hard drive remotely if recovery seems unlikely. Tools like Find My iPhone offer similar features to smartphone and tablet users. Install them before your device goes missing.
Video surveillance systems
The all-seeing eye of a camera won't prevent determined thieves from breaking into your office, but remote surveillance systems may help you catch them red-handed. Video surveillance with motion detection will show the scene of a crime in real-time and record footage to help you pursue the bad guys later.
Fire, floods, and acts of God
We've dealt with thieves, but what about interventions of overwhelmiong magnitude? The general preparedness tips outlined above--especially the use of offsite backups--will help mitigate damage due to natural disasters, but a few devices can do even more, if you're concerned that a fire or flood might whisk away your life's work.
For digital storage, ioSafe makes a range of external hard drives designed to resist both fire (at up to 1550 degrees Fahrenheit) and water (a water column of up to 10 feet for 3 days). Keep analog essentials such as paper documents (and printouts of essential data) either offsite in a safe deposit box or in a sturdy fire safe on the premises. These inexpensive safeguards are well worth the investment.