We've Told You Ten Times: Get A Bigger Monitor
Researchers at the University of Utah tested how quickly people performed tasks like editing a document and copying numbers between spreadsheets while using different computer configurations: one with an 18-inch monitor, one with a 24-inch monitor and with two 20-inch monitors. Their finding: People using the 24-inch screen completed the tasks 52% faster than people who used the 18-inch monitor; people who used the two 20-inch monitors were 44% faster than those with the 18-inch ones. There is an upper limit, however: Productivity dropped off again when people used a 26-inch screen. (The order of the tasks and the order of computer configurations were assigned randomly.)
The beauty of this study is you can get your boss to pay for your bigger screen. Tell him it's science, after all. But remember, when your work monitor is finally the size of a drive-in movie screen, be careful clicking on those NSFW links at lunchtime, OK?