Ergonomic products such as keyboard, mouse, and mousepads are a good investment since they provide the wrist support to prevent strain and repetative motion injuries.  Lighting is also important, and the investment into a couple of good architect lamps will pay off immensely.  Drawer and desktop organizers make finding pens, pencils, paper clips, and other small office tools easy.  Media storage cabinets and racks makes organizing diskettes, CD's, and backup tapes easy, and wallmount models are both attractive and extremely practical for the small home office.

If your office is already equipped with a scanner and printer, and your computer is on a modem, you really don't need to add a fax machine or telephone to your office.  A good headset microphone and the telephony software is all you require, with some packages offering voice mail and faxback tools.  Any function or task that can be handled by your computer should be assigned to your computer rather than adding another component that will require additional space and energy.

Your equipment should and must be kept out of direct sunlight and away from any heat source, this is especially important with printers and photocopiers.  Your work area should be cooled so as not to overheat your computer system, in Summer months air-conditioning is recommended since your computer is going to be happier with a cooler or cold environment.  If working with laser printers and copiers, your area must be well ventilated to prevent the effects of ozone given off by such units.  Laser equipment must be well maintained, this includes being operated in a dust and smoke free environment, cooler room temperatures with minimal humidity, and away from light and heat sources.

One of the best investments you can make will be in a good UPS.  There is nothing more frustrating or counter-productive than losing work to a power failure, surge, spike, or brownout.  It is not recommended that your UPS is used as a suppliment to your power, it is there to provide you adequate time to save your work and power down your system properly.  A good UPS will also help protect your equipment and investment, your system will remain stable for longer periods of time and will not suffer equipment failure because of an energy spike or dip.