I first got organised about 18 months ago with a second screen.
It has made a dramatic difference to my productivity and overall work enjoyment. The key for me is to be able to have maybe 3 or 4 windows open at once and to be able to read one document, whilst creating another. Typical examples would be report/ blog writing or entering notes into a CRM system from other inputs. It makes cutting and pasting so much easier.
Various studies have also confirmed significant productivity improvements.
Microsoft claims productivity improvements of between 9 and 50% – see report here
An NEC productivity study conducted by the University of Utah confirmed these findings but noted a decline once the screen becomes too large. Here is the link to download the NEC Productivity Report (pdf)
An additional step that I have taken to improve my workspace is to get a wireless keyboard and mouse which reduces clutter even further.
To start using two screens you will probably need a new video card which will cost you maybe $100, then you simply plug the second screen in.
The required training is absolutely minimal – the user will quickly discover an approach that works for them. Several other clients and colleagues have confirmed the advantages of two screen and I highly recommend it as a quick, affordable productivity step.