So Activision is not the most beloved publish at the moment. Maybe you hate them so much you don't want to buy any of there games at the moment? Maybe you don't even want to play there current games? Here is a list of some alternative games that Don't have the Activision logo and won't give them any more of your cash.
Instead of Guitar Hero try...
Rock Band two is my absolute favorite music game, everything about it just feels amazing. From the world tour mode to all of the songs they have its just a better overall experience then guitar hero. (imo) One of the amazing things about the Rock Band Franchise is how if you buy rock band 2 you can rent Lego rock band, or rock band 1 and rip all the tracks to Rock Band 2 so you don't have to disk swap. The only exception is Rock Band Beetles but all of the other games work, and Hamonix will most likely continue this into Rock Band 3 so buy away and remember that you can bring those songs to the next game.
Instead of Modern Warfare try...
I like playing a game tactical and no other shooter does tactical game play like bad Company 2. The maps are huge, the gameplay is awesome, and battlefield has so many "epic" moments that you will be finding yourself saying wtf multiple times. (In a good way)
But if you are into run and gun shooters or Battlefield does not click with you here are some honorable mentions.
Rainbow six Vegas 1/2
Gears of War 1/2
Instead of Tony Hawk try...
First off if you bought the new tony hawk ride and had hope that it was going to be good then let me be the first to say I'm sorry. But fear not the Skate series is pretty damn good. Skate is not like the "regular" tony hawk games. You use the analog sticks to do tricks. (flip the stick one way or another) Its easier to get used to the Ride, but its not as easy as clicked a few buttons. On the other hand once you are able to pull off tricks one after another its very rewarding.
I can't get this damn image to resize, my bad.
Instead of World of Warcraft try...
Outside is this amazing world that... Ok haha I had my fun but in all seriousness i can't recommend 1 MMO because there are so many, and not everyone likes the same things I would have to list off a few that I have liked in the years of playing MMO's.
Star Trek Online
Ever Quest 1/2
Age of Conan (try the trial)
Or you can wait for Biowars new Star Wars MMO. (which I myself with ditch WoW for)
So there you go, there are a few suggestions for different games to play. I know its hard to quite MW2 and Guitar hero cold turkey, BUT there are some really good alternatives out there. Activision is being a little bitch and cheating gamers out of there money. They are destroying the industry and I hope no one here buys the 15 dollar map pack....
Side note: Blizzard is a good company so you don't HAVE to stop playing there games. In fact I'm going to buy Diablo 3, starcraft 2, and the new WoW expansion when I get the chance, BUT if you want to quit activision then those are some alternatives for MMO's.