I say there could be numerous definition to the subject heading but the specific criteria here is that if the game was released tommorrow, it could manage to sell more than one million copies first week in a single territory.

My top ten would be:

1.GTA

2. Pokemon

3.Gran Turismo

4.Super Smash Bros.

5.Mario Kart

6.Halo

7.Final Fantasy

8.Dragon Quest

9.Monster Hunter

10. Super Mario.

Edit-Oh now, I wish you can edit the title. Think, not thing.

very nice list

extreme lack of zelda, otherwise good list.

The top 10 franchises today? That's incredibly easy!

1. Wii

2. Mario

3. Pokemon

4. The Sims

5. Training (Brain, Sight, Face, etc.) 

6. Grand Theft Auto

7. Gran Turismo

8. Guitar Hero

9. Call of Duty (if Call of Duty 4 is any indication of the future of the franchise)

10. Final Fantasy

Obviously this list is disputable. The Final Fantasy franchise has sold a lot more copies of games than the Wii franchise, but this list refers to what this generation has shown or may show. After #5, it's a lot harder to make the list.

My top 10:

1.- Pokemon
2.- GTA
3.- Smash Bros
4.- Mario Kart
5.- Super Mario
6.- Halo
7.- Zelda
8.- Gran Turismo
9.- Final Fantasy
10.- Dragon Quest

Yeah, Ok but I added a criteria which I should have made more noticeable. Sorry. I mean what are the top ten that can sell over a million copies in just one territory *whoops-edit* IN THE OPENING WEEK. That's why I didn't put in Zelda because I wasn't sure it could do that today. I also have some serious reservations about Call of Duty 5's ability to breach over a million knowing who's making it.

 I don't know, I think Mario Kart would belong in the Mario franchise.

1.GTA
2.Halo
3.Zelda
4.Wii
5.Mario
6.Final Fantasy
7.Call of Duty
8.Metal Gear Solid
9.Dragon Quest
10.Monster Hunter

11. God of War

mmmmm, I think you are correct, my new list.

1.- Pokemon

2.- Super Mario(with mario kart and mario sports)

3.- Wii

4.- GTA

5.- Smash Bros

6.- Halo

7.- Zelda

8.- Gran Turismo

9.- Final Fantasy

10.- Dragon Quest