A couple years back I managed to get two identical monitors. At 130€ a piece it wasn’t so cheap to get, but now I think it was the best buy in ages.
Since then, my productivity increased 10-fold. That, allied with Windows 7 and Compiz ease of putting windows side by side, gave me the ability to put 4 windows side-by-side allowing me to see all the information that I needed to do my work.
Unfortunately, the main downside is that it takes quite some space from my desk. 2 20 inch screens are quite big! However given that my computer is my main working tool, it’s well worth it!

