No matter what card you buy today you will have to upgrade it in 3 years MAX.
Assuming you do not accept anything less than high or ultra graphic settings.
My Radeon HD 5850 is 3 years old now and it is still capable of playing games today (1920x1200 resolution). I'm not a hardcore gamer so medium graphics quality is fine. If I don't get enough performance with everything set to medium quality, then I'll upgrade.