There has been only about one game per year that really pushes a PC. The most demanding games right now are Crysis: Warhead (2008), Metro 2033 (2010) and BF3 (2011)
maybe it's just me, but i don't buy every game. so the next best game, graphically speaking, may never reach my hard drive. i buy a new FPS game that i really like once every other year. IMO buy a card that processes well what you enjoy playing today. worry about the "next best thing" when you really think you need it, whether that be a game or a video card. for some people that could be 6 months or five years.