Basically, if you’re a home worker, or run a small business, don’t go cheap on the tools you use the most.
If you’re on the phone all the time, get a nice phone and headset. I just received the Calisto Pro for being a finalist in the Telewho contest. It’s pretty sweet.
If you’re on the computer all the time, do some research into whether a Mac or PC would work best for you, spend the money you need to, and don’t skimp on the accessories. Get a good monitor, get a nice bag or sleeve for your laptop if you’re mobile.
Really though, the important thing is not to skimp on the important stuff. I rarely print, so I bought a cheap printer. I do a lot of web design, photography and video, so I bought an iMac and a Drobo. Expensive, but very much worth it for my productivity and the quality of my output, as well as data security.
It’s your business. Don’t cheat yourself out of quality to save a few bucks. If you are cheap now, it’ll eventually show up in your product/service. If you spend for quality now, it will eventually be reflected in the high quality of your product/service.