The most recent paradox newsletter announced that they're offering a tenth anniversary discount 50% off their entire range except East india company/Hearts of Iron III until the 26th of July. This one looks like the best saving, but see the first reply for other links and a demo for EU3.
Europa Universalis III - Complete
Delving deep into the areas of exploration, trade, warfare and diplomacy, Europa Universalis III is an epic strategy game where players take control of a nation and guide it through the ages to become a great global empire. Unparalleled in its depth and historical accuracy, EU gives players freedom to rule their nation from an impressive choice of over 250 historically accurate countries.