After careful consideration, I've revised my earlier list of top killer apps. Note that this is not my preferences for what killer app I like, but what I feel has the most influence. On that note, I disqualified anything from this gen, since it's too soon to tell their influence.

BTW, I know being a killer app isn't about being influential, just about getting interest in the system a particular app is on. The thing is that a some killer apps can do so much more than that. WordPerfect was a killer app for DOS, but that was clearly just the beginning for that system.

Basically, I'm ranking this list based on how "killer" the apps are.

And remember that a bestselling game is NOT the same as a killer app. It has to get people to want that system, or concept, just for that application. Thus Super Mario 3 is not a killer app, as most people had already heard of the NES when they bought it.

But before the top ten, here're are a few honorable mentions.

Best killer app of this gen: Wii Sports/Twilight Princess.

In Japan and North America respectively, those games have sold at least half as many games as systems sold. That shows how many people are buying the Wii just for those games.

Best killer app for High Definition: Gears of War.

Yes, Resistance had graphics that were also highly detailed, and gameplay just as intense, but Insomniac didn't think to liscense their game engine, while Epic did. This is important, as few developers considered the cost of HD gaming at first, and with the Wii selling so well, the cost looks even worse. Thus the cost saving of game engines has become even more important, and Gears was a perfect showcase for making such a game for far less than a game of that scale.

Most embarrassing attempt at a killer app:

Well, I actually would like your input on this. So far, I can just think of Halo 2 Vista, but there are likely others.

Now onto the the top ten killer apps in gaming.

10. Sonic the Hedgehog.

Why it's on this list: This is a good example that a killer app does not have to be a launch game. Sega wasn't a serious contender in the console business until this game out. Sure the Genesis had some decent sales, but not to the level of after this game.

Why it's #10: Unfortunately for Sonic, he couldn't help Sega from screwing themselves over.

9. GTA III.

Why it's on this list: The PS2 would have been a success without this game, as hits like Devil May Cry, Gran Turismo 3, and Metal Gear Solid 2, came out that same year. This game, and it's follow ups, ensured the PS2's dominance in the 6th gen, and helped it sell better than the PS1.

Why it's #9: As I stated, the PS2 already had hits, so this wasn't as much of a killer app as the other games on this list.

8. Nintendogs/Brain Age.

Why they're on this list: There are a lot of excuses for why the PSP isn't overtaking the DS (like the supposed monopoly of Nintendo in handhelds), except for the real one: it doesn't have a true killer app yet (plenty of bestselling games, but no real killer apps), while the DS had two within a year.

Why they're #8: Although these are two of the bestselling examples of casual games, and respectively pet simulators and edutainment games, those genres are nothing new.

7. Pokemon.

Why it's on this list: How many game series can boast they're killer apps for three gaming systems (#8 may be why it's not for four systems)? Sure the Gameboy, GBC, and GBA were already hits, but a lot of gamers holding out scooped up the systems one these games came out for their respective systems.

Why it's #7: Again, those systems were already hits.

6. Halo 2.

Why it's on this list: There's a reason Halo 1 isn't on this list, and it's the same reason Smash Bros Melee isn't here. Despite being bestselling games, and clear killer apps, thier systems didn't sell that well. Halo 2 isn't here just for the Xbox, which a lot of people did buy it for, but also for Xbox Live. The service was 2 years old when Halo 2 came out, but the game doubled its adoption rate, and set some standards that were incorporated in the 360's version of Live, thus helping it beomce the gold standard for online services (although it should be, considering it's a pay service).

Why it's #6: I guess it's just that Halo 2 came out less than three years ago, so given more time, and a great enough growth of the Xbox brand and XBL, it may be higher on the list.

5. Goldeneye

Why it's on this list: Sure the Nintendo 64 had a killer app with Mario 64, but first of all, this game was a killer app after the developer defections started to take a toll on the system's library. Second of all, there are a couple of other reasons this game is on the list. For one, this game, and Mario Kart 64, were the first true smashes in multiplayer gaming on consoles, although having four controller ports built in helped. For another, FPS was not a serious genre on the console. Mostly, there were ports of PC FPS games (aside from Doom 64 being made for a console). After this game, the genre was shown to be viable on consoles.
Now some may insist that Halo 1 was the true breathrough for console FPS, but most of their arguments show that they think only a few FPS games came out between Goldeneye and Halo, and that they think Halo's dual analog control came out of the blue, as though developers hadn't beem moving towards such a control since Doom on the SNES used the shoulder buttons for strafing.

Why it's #5: First of all, this game didn't gain the N64 any lost ground; it only stopped it from losing more. Second, FPS were nothing new, even on consoles.

4. Final Fantasy VII

Why it's on this list: Let me count the ways: 1) RPGs were a niche genre in the west, until this came out. 2) This showed the value of optical discs over carts (except in handhelds, and even then, those carts aren't the bulky, expensive kind). 3) The mere announcement, of this game going to the PS1, led a wave of support for the system, and the rest is history (as in you look it up; I shouldn't have to tell you ;) ).

Why it's #4: Simply put, it didn't change the face of gaming like the top three (although it did set a lot of standards for presentation).

3. Super Mario Bros.

Why it's on this list: If I have to tell you, you wouldn't get the rest of this list anyway.

Why it's #3: Well the west was only one region, and it took years to become a bigger market than Japan.

Tetris (Gameboy Grayscale)

Why it's on this list: Handheld gaming was limited to those Tiger LCD games, which were fun (and could make an interesting compliation on the DS and PSP), but could only do so much with the games. In 1989, technology allowed true handheld gaming, and thus we had the Lynx and the Gameboy Grayscale (which it should be called, since that gives it a proper three letter abbreviation ;) ).
The Lynx unfortunately didn't last long, but the GBG showed us the next era of handheld gaming (from then to now), thanks to a great battery life AND games like Tetris, which is almost the perfect handheld game, in that it's game structure allows you to get how to play in as little as five minutes, but you could play for hours if you felt like.

Why it's #2: I first had it at #1, but then I realized the success of handhelds was partly due to this game, but also due to Gunpey's ingenious design philosophy of battery life over graphics (although the GBG does have better spriting power than the NES). Plus not every handheld game needed to follow its standards to be hits. Super Mario Land needed a fairly long playing time, but it was a definate hit.

Virtua Fighter 1/Mario 64

Why they're on this list: It's not for their systems (VF1 started out as an arcade game anyway). It's for changing the face of gaming. Again, a killer app is to get interest in something, and this case, it wasn't for any one system. It was for just about every 5th, 6th, and 7th gen home system, and the 4th gen handhelds, not to mention Direct X.
Sure these games weren't the first 3D polygon games, but VF1 actually got developers excited about this kind of graphics, and Mario 64 not only set a lot of standards for "full 3D" (free exploration and a mostly free camera), but also showed that a game series didn't have to start in 3D to work.

Why they're #1: Let me make it clear. These two games bookend an transition that changed the face of gaming.

Biggest killer AP failure: Gundam Musou and Motorstorm. Sold well but were far from reaching the status they were hyped too.

Luigi's Mansion.

In terms of failure to be a killer app, the entire Resident Evil lineup for the GCN, which seemed to do nothing to help sales.

Anyway....

Not a bad list. Doubt I could compile a better one, though I'd likely put SMB to #1, simply because it was one of the first arcade games to be accurately ported to a home console, and it pretty much sold the NES which then salvaged the gaming industry. At least that's how I see it.

 Super Mario 1 was remade for the arcades well after the NES version (it incorporated some of the areas from Lost Levels), and even if it was an arcade port, Street Fighter II on the SNES was more of a killer app of that type.

good list, I'd have it quite similar I think.

Great list, though I would have probably ranked GTA higher. Despite the fact that there were other good games on the PS2, they didn't appeal to the casual market. GTAIII was the first true example of a casual system seller.

Pong and/or Pacman didn't make your list and that completely invalides it.

Any list that ignores the birth of console gaming is... ah... missing something, to say the least.