I did a look at GameStop's US Website today and came up with a list of games from now until Xmas with their "GameStop" release dates for PS3 and 360...  I excluded all games that are coming out on both platforms before Xmas and any games that are already (or will be) on one platform but is going to be released on the other before Xmas (Ex. GRAW2, DiRT, Stranglehold).  Finally, I excluded a lot of the 1st of the month games because that usually means it really isn't coming out and they just have the date to have one.  But, I did include it certain cases because the game is known to be coming out some time in that month or before Xmas.  It should be noted that the list is "as-of today" and Gamestop is not the definitive site for this info. but they do seem to have a pretty good handle on what is coming out and when as they are one of the largest retailers.

Looks like Xmas will be fun for NextGen fans... Looks like 360 will have a quantity lead on PS3 but that doesn't necessarily lead to quality... (I didn't include Wii because almost every game is unique on it and I don't really see it competing with Playstation 3 and Xbox 360 directly... Its in a class on its own.)

Here is the list month by month:

August:
360
Two Worlds (14th)
BioShock (21st)
Moto GP '07 (27th)
Blue Dragon (28th)

PS3
Lair (14th)
Warhawk (28th)

September:
360
FlatOut: Ultimate Carnage (4th)
Fatal Interia (11th)
Kengo Legend of the 9 (11th)
Project Gotham Racing 4 (11th)
Eternal Sonata (17th)
CSI Hard Evidence (18th)
Looney Tunes Acme Arsenal (18th)
Warriors Orochi (18th)
America's Army (25th)
Cabela's Trophy Bucks (25th)
Halo 3 (25th)
Hot Wheels Beat That (25th)

PS3
Heavenly Sword (4th)

October:
360
Crash of the Titans '07 (2nd)
Spiderman: Friend or Foe (2nd)
Beautiful Katamari (15th)
Thrillville: Off the Rails (15th)
Avatar: Buring Earth (15th)
Chessmaster Grandmaster Edition (16th)
Naruto (16th)
Ace of Combat 6 (23rd)
Cars: Meter-national (23rd)
Tomb Raider Anniversary (23rd)
Viva Pinata Party Animals (23rd)
Bee Movie (30th)

PS3
Eye of Judgement (1st)
Hot Shots Golf (1st)
Ratchet and Clank: Tools of Destruction (2nd)
Folklore (9th)
SingStar (30th)

November
360
Mass Effect (1st)
FEAR Files (6th)
World in Conflict (7th)

PS3
Unchartered Drake's Fortune (1st)
Unreal Tournament III (1st)
Haze (20th)
Time Crisis 4 with Guncon (20th)

December
360
Nothing to Note

PS3
Grand Turismo HD (1st)
MX vs. ATV (19th)

To be honest only PS3 games to really put up a fight with 360 in MONTH OF LAUNCH are Haze & UTIII, but I think the delay for Haze's Launch on 360 is actually a good thing since there are so many FPS games launching for the 360 during the Xmas months.

GT-HD will sell well though and Time Crisis gcould fight back, but 360 will own September & November.

Since it looks like you forgot something since you're doing a "Next gen" list.

August
Wii
Boogie (7)
Carnival Games (27)
Metroid Prime 3: Corruption (27)

September
Wii
Dewey's Adventure (4)
Fishing Master (10)
Cosmic Family (18)
My Sims (18)
DDR: Hottest Party Bundle (25)
Backyard Football (26)

October
Wii
Clash of the Titans (2)
Spiderman: Friend of Foe (2)
Donkey Kong: Barrel Blast (8)
Bleach: The Shattered Blade (9)
Tony Hawk's Probing Ground (9)
Avatar: The Burning Earth (16)
Nicktoon: Attack of Toybots (26)
Battalion Wars 2 (29)
Need For Speed: Pro Street (30)

November
Wii
High School Musical: Sing It! with Microphone (6)
Geometry Wars: Galaxies (6)
Ghost Squad (6)
Super Mario Galaxy (12)
Resident Evil Umbrella Chronicles (13)
Rayman: Raving Rabbids 2 (13)
Soul Calibur Legends (13)
Trauma Center: New Blood (13)
WWE Smackdown VS Raw 2008 (19)
Mario and sonic Olympic Games (20)
CSI: Hard Evidence (27)

December
Wii
Super Smash Bros Brawl (3)
The Golden Compass (4)

About 5 of those 360 games are movie games, that are coming out on the ps3 too... But gamestop doesnt have those games listed for the ps3 for some odd reason... And they had the date of unreal being released first on the 360..as well as haze : (

Halo 3 alone may outsell all of the PS3 games through October.

I thought it was odd the "movie" games weren't listed as well but I didn't want to put something unless it was actually there...

I made the adjustment in my list for Unreal and Haze...  Unreal and Haze aren't coming until next year for 360 so that's why their listed for PS3...

Purposely excluded as stated in original post.  Wii is unique and therefore doesn't really compete with Sony and Microsoft.  They are going in a different direction (a good direction, but different so a comparison is really not necessary).   

 Gross!

but Wii games do compete with the 360 and PS3 games.

The games I'm looking at this holiday season:
Mario Strikers (Wii)
Bioshock (360)
Metroid Prime 3 (Wii)
Assassin's Creed (360)
Mass Effect (360)
Blue Dragon (360-- a little iffy after playing the demo)
Eternal Sonata (360)
Super Mario Galaxy (Wii)
Super Smash Bros. Brawl (Wii)
Unreal Tournament 3 (PC-- I can hope it comes out this year)
Boogie (Wii)
Brothers in Arms: Hell's Highway (PC)
Madden 08 (Wii)

That's a lot of games and I can't get them all. I have to decide which ones I want so these games (Wii, 360, and PC) are all competing with each other. Right now I can narrow that list down to 6 (MSC, Bioshock, MP3, Mass Effect, SMG, SSBB) but I need to narrow it down to 5 so I'm having a pretty tough deciding which of those games to cut.

 lol whoops