The Positional Exchange Sacrifice Done Right
If you like positional chess, you definitely should learn the art of the positional exchange sacrifice. It's more difficult than it looks, though; I can personally attest that I lost many games from getting too fancy and sacrificing the exchange for what turned out to be nothing at all. Done right, though, the positional exchange sacrifice is an awesome way to win.
If you're looking for GM examples, check out the games of Petrosian, Karpov, and Kasparov (contrary to popular belief, Kasparov's sacrifices were mostly positional, not tactical.) If you're looking for a lower-level example, though, check out the following 3-minute game.
With 23. Nc4, my opponent was expecting to kick my rook out of e3, leaving him in a fine position. But he missed the positional exchange sacrifice!
This game is also instructive when it comes to king marches in closed middlegames--they can be quite effective, and are always fun!