If you're running a small business, you probably can't afford the expense of a professional office planner, nor even the time it will take to plan out the best use of your space. One tool that I've used is Ikea's Office Planner, a free download that makes short work of placing desks, chairs, and storage units into a virtual office space. You just enter the dimensions of your room and drag images of office furniture into a 2D or 3D representation of it. Of course, all of the furniture is Ikea's. When you're done with your plan, the program will print out a shopping and price list.
You can do similar things with a drafting product like Visio, but the Ikea software is marvelously simple. Likewise, Ikea furniture is easy to buy. This is a great tool.