IKEA is not a company we ordinarily associate with software, but it does know to sell office furniture, and to that end there's a handy little download on its web site called the IKEA Office Planner. It's a free app for Windows that lets you visualize the physical layout of your office, drag and drop models of furniture into it, and see it rendered in 3D. Of course, the whole point of the exercise is to get you to buy IKEA's flat-pack wares, and it'll even tally up the price of all your 3D furniture for you, but you could also just use it to get a feel for how much desk you have room for before hitting Office Depot.