MS didnt really have a huge game to attack ps3 this year.
next year, im guessing Killer Instinct 3

Sorry to quibble, because I know what you meant, but none of Gears 1, Halo 3 or Gears 2 are killer apps. Wii Sports is a killer App, and Wii Fit could possibly be considered one

"A killer application (commonly shortened to killer app), in the jargon of computer programmers and video gamers, has been used to refer to any computer program that is so necessary or desirable that it provides the core value of some larger technology, such as a gaming console, software, operating system, or piece of computer hardware." - wikipedia

None of the three games you mentioned fulfill that criteria.

Some Killer Apps in the past and their effect
The combination of a killer spreadsheet app and the first GUI took Apple from a tiny company to having a majority of computer marketshare over the space of a few years
Microsoft Office was a better killer app, and gave Windows the ridiculous marketshare they have today
Wii Sports - the console that was predicted to sell 15 million lifetime should sell 10 times that.

Are you putting something like Halo 3 in the same league as Wii Sports and Microsoft Office?

First of all, Wii sports is bundled, and will easily be the biggest video game in history in any list that doesn't disqualify it from. But hardly a fair basis for comparison. (If being a killer app is relative, by the end of the Wii's lifecycle, only Wii Sports/play will count)

Also, comparing games to MS office is ridiculous - office productivity tools used by home users as well as a large % of the world's companies obviously can't be compared against. No game will ever have sales approaching Microsoft Office's LTD sales - including Wii Sports.

Killer apps, as they are described now, are the top video games of the time, generally they come with hype, and need to live up to that hype (somewhat) to qualify. As such, all 3 halo games and both GeoWs count as killer apps.

Microsoft won't let us 360 fans down, something big planned!

Keep in mind that nearly all the best selling games this gen are multiplayer. The top single player HD game this gen so far has been Assassins Creed, and it would have sold much less on a single platform (not quite Halo 3 / GeoW2 level). I'm not sure how Alan Wake is going to be like, but it sounds like a single player deal to me, which limits its impact.

It'll be interesting, though. Will the top selling PS3 exclusive of 09 top the 360's? For the first year it may happen, if GT5 is brought out.

A fighting game will never be the big hitter for any company.

A Killer App is not related to how many sales it gets

The original definition of the term meant a piece of software that it was impossible to live your daily life without.

Back before Open Office and Google docs, you had to use Microsoft Office if you had an office job. There was no saying "I don't like Microsoft Office, I'll not use it" Therefore it was a killer app

Now us gamers got to the phrase, and changed it to a piece of software that differentiated a console from itts competitors. I haven't to break it to you, but all three of these 'killer apps' are shooters. Shooters are not a way to differentiate yourself.

If you are using Killer App to mean 'a popular video game' then you are wrong, that's just not what those words mean

 I'd be inclined to say Mass Effect 2. Mass effect had some hype, but was a new IP - lots of people, including myself didn't know much about it, and ended up blown away by the eventual product. Reviews were great, and so was word of mouth. (A friend convinced me I HAD to buy it, and I've convinced at least 2 more) Because of it's lack of Multiplayer however, unlike a game like Halo 3, where everyone plays it together, a lot of people went through it multiple times, and then loaned it to friend to do the same. However I anticipate the sequel coming with a decent fanbase, and less people willing to wait for their friends to make 3 playthroughs before trying it. First one had 2 million or so sales WW, I'd anticipate some decent growth for the next one. (Especially with the 360's install base looking to have grown by well over 10m since ME's release - and if it released on 360 again ahead of the PC, expect some of those hooked on the PC version to be unwilling to wait and pick it up on the 360.

That may be possible for the Wii, however I think Sony can't keep their collective mouths shut about anything.  Thats why they talk up games 4 years out ( which still pisses me off severely).

I will have to go with Mass Effect 2 or Conan MMO.  I loved the first ME so much, and had atleast 3 or 4 of my friends hooked as well.   I don't know the release date when Huxley is supposed to come out, but I am really looking forward to it as well.  I think it has a lot of potential.

Mass Effect 2, Halo 3: ODST, Halo Wars, Alan Wake, Forza 3, Call of Duty Modern Warfare 2 (multi, but the 360 will get the most sales), + 7 unannounced titles