What kind of games do you play?
What is the rest of your system?
Without knowing these it is hard to make a good recommendation but if you want a card that will last ~2 years you are going to have to go with at least a Radeon HD 3850. Anything else will just come up seriously short within a year (or less).
Of course, this also depends on what the rest of your system looks like (will your processor adequately push a 3850 and do you have adequate memory) and what kind of games you play (if all you play is WoW and you don't intend to play anything more demanding, a 7600GT or x1900/x1950 will be just fine).