I started thinking about what new franchises have been created in this seventh generation of gaming. Here's a list of new games that began on either the PS3/360/Wii and have a sequel either already released or confirmed to be in the works.  I consider this different than just a new IP. It must have a confirmed sequel. Make what you will of this data. Corrections are welcome.

PS3 has 4 new exclusive franchises (Resistance, Heavenly Sword, MotorStorm, Uncharted) and 7 multi-platform new franchises.

360 has 5 new exclusive franchises (Gears of War, Viva Pinata, Prey, Mass Effect, Dead Rising) and 7 multi-platform new franchises.

Wii has 6 new exclusive franchises (Wii Series, Red Steel, Trauma Center, Elebits, Boogie, Game Party) and 2 multi-platform new franchises.

PS3
Resistance
Uncharted
Heavenly Sword
MotorStorm
Assassin's Creed (mp)
Saints Row (mp)
Skate (mp)
Condemned (mp)
Rock Band (mp)
Bioshock (mp)
Rainbow 6: Vegas (mp)


360
Gears of War
Prey
Viva Pinata
Mass Effect
Dead Rising
Assassin's Creed (mp)
Bioshock (mp)
Saints Row (mp)
Condemned (mp)
Rainbow 6: Vegas (mp)
Rock Band (mp)
Skate (mp)


Wii
Wii Series (Wii Sports, Wii Play, Wii Fit)
Elebits
Boogie
Red Steel
Game Party
Trauma Center
Rock Band (mp)
Skate (mp)


Other notes:

Wii:
Disaster (I'm assuming if this is successful, there will be a sequel)
The Wii series (as in Wii Sports, Play, Fit, Music, etc.)
Rayman Raving Rabbids (It's essentially its' own series, as the Rabbids are really the stars)
Trauma Centre
Zack and Wiki

360:
Assassin's Creed
Tom Clancy's EndWar
Mass Effect
Scene It (New to video games)

PS3:
Assassin's Creed
Tom Clancy's EndWar
Little Big Planet

Wii:

Lost Winds (WiiWare, but it still counts, right?)


I believe 360's Too Human is going to be a franchise too.

Lost Odyssey:Mistwalker is going to make a sequel to this game along with Blue Dragon

^lost winds does b/c it has a sequel already planned

also dont forget excitecite truck

The Last Remnant has a chance of becoming a series if you consider those new trademarks SE has registered

hey you missed Tom Clancy's Hawx it's coming out this fall.... kameo can go there too....

You missed out Motorstorm and Heavenly Sword.

thekitchensink: I wasn't sure whether to include Trauma Center since the original game started out on the DS. Wii Series is a toss-up but they're all different games. I'll wait until they announce Wii Sports 2 or Wii Fit 2. Rayman is a spin-off so I decided not to include it. No confirmed sequels for Z&W or Disaster, Assassin's Creed, LBP, Scene It, EndWar.

Updated with Mass Effect and Lost Winds.

Nah, the Wii series is definitely a franchise. They all focus on different things but mechanics and philosophy are unified throughout the series. If anything, it's the most successful new franchise of the 7th gen (so far).