(For the newbie: a multiplatform game, aka cross platform, is when a specific game is made for different systems.)

When 360 and PS3 multiplatform games are pitted against each other, using a variety of hardware tests including framerate, resolution, loading times, and graphic effects, the results can be surprising. Being unbiased myself (I do not own 360 or PS3, nor do I plan on buying either) I find eurogamer to be a good source of these comparisons not just because of their rigorous tests, but because they allow you to judge for yourself with screenshot and video comparisons. You can view them all here:
http://www.eurogamer.net/article.php?article_id=318609

Special thanks to Mister Slimm who keeps an updated list of the following results here:
http://misterslimm.wordpress.com/2008/11/06/eurogamer-xbox-360-vs-ps3-head-to-head-face-off-results/

The Epic Battle
Format:
(Game name ~ Better Platform)

Army of Two ~ Tie
Assassin’s Creed ~ 360
Baja: Edge of Control ~ 360
Battlefield: Bad Company ~ Tie
Beijing 2008 ~ 360
Beowulf ~ Tie 
Bioshock ~ 360
Blacksite: Area 51 ~ 360
Bladestorm: The Hundred Years’ War ~ Tie
Blazing Angels: Secret Missions of WWII ~ Tie
Blazing Angels: Squadrons of WWII ~ 360
 Brothers in Arms: Hell’s Highway ~ Tie
Burnout Paradise ~ Tie
Call of Duty 3 ~ 360
Call of Duty 4 ~ Tie
Call of Duty: World at War ~ 360
Cars Mater-National ~ Tie
Clive Barker’s Jericho ~ 360
Colin McRae: DiRT ~ PS3 
Conan ~ Tie
Condemned 2: Bloodshot ~ 360
Conflict: Denied Ops ~ 360
Dark Sector ~ 360
Dead Space ~ 360
Def Jam: Icon ~ Tie
Devil May Cry 4 ~ Tie
Dynasty Warriors: Gundam ~ Tie
Dynasty Warriors 6 ~ PS3
Enchanted Arms ~ 360
Enemy Territory: Quake Wars ~ 360
FaceBreaker ~ 360
 Far Cry 2 ~ Tie
Fallout 3 ~ 360
Fantastic Four: Rise of the Silver Surfer ~ 360
F.E.A.R. ~ 360
FIFA 08 ~ Tie
 FIFA 09 ~ Tie
FIFA Street 3 ~ 360
Fight Night Round 3 ~ PS3
 Fracture ~ 360
Grand Theft Auto IV (GTA IV) ~ 360
Guitar Hero: Aerosmith ~ 360
Guitar Hero III: Legends of Rock ~ 360
 Guitar Hero: World Tour ~ 360
Half-Life 2 ~ 360
Half-Life 2: Episode One ~ 360
Half-Life 2: Episode Two ~ 360
Harry Potter and the Order of the Phoenix ~ PS3
Iron Man ~ 360
Juiced 2 ~ 360
Kane and Lynch: Dead Men ~ 360
Kung Fu Panda ~ 360
Lego Indiana Jones: The Original Adventures ~ 360
Lego Star Wars: The Complete Saga ~ Tie
Lost: The Video Game ~ 360
Lost Planet: Extreme Condition ~ 360
Madden NFL ‘08 ~ 360
Madden NFL 09 ~ 360
Marvel Ultimate Alliance ~ 360
Medal of Honor: Airborne ~ 360
Mercenaries 2: World in Flames ~ 360
Midnight Club: Los Angeles ~ 360
 Mirror’s Edge ~ Tie
MX vs. ATV Untamed ~ 360
NBA 2K7 ~ PS3
NBA Live 08 ~ 360
NBA Street Homecourt ~ 360
Need for Speed Carbon ~ Tie
Need for Speed ProStreet ~ 360
NFL Tour ~ 360
NHL 2K7 ~ Tie 
NHL ‘08 ~ 360
NHL 09 ~ Tie
Oblivion, The Elder Scrolls IV ~ PS3
Overlord: Raising Hell ~ 360
Pirates of the Caribbean: At World’s End ~ 360
Portal ~ Tie
Pro Evolution Soccer 2008 ~ Tie
Pure ~ Tie
 Quantum of Solace ~ Tie
Race Driver: GRID ~ 360
Ratatouille ~ Tie
Ridge Racer 6 /7 ~ PS3
Sega Rally ~ Tie
Sega Superstars Tennis ~ Tie
Skate ~ 360
Soldier of Fortune: Payback ~ 360
Sonic the Hedgehog ~ 360
Soul Calibur IV ~ 360
Spider-Man: Web of Shadows ~ 360
Spider-Man 3: The Game ~ 360
Star Wars: The Force Unleashed ~ 360
Stranglehold, John Woo Presents ~ Tie
Stuntman Ignition ~ 360
Team Fortress 2 ~ 360
The Bourne Conspiracy, Robert Ludlum’s ~ Tie
The Club ~ 360
The Darkness ~ 360
The Godfather ~ PS3
The Golden Compass ~ Tie
The Incredible Hulk ~ PS3
The Simpsons Game ~ Tie
Tiger Woods PGA Tour 2007 ~ Tie
Tiger Woods PGA Tour 09 ~ 360
Timeshift ~ 360
Tom Clancy’s Ghost Recon Advanced Warfighter 2 ~ 360
Tom Clancy’s Rainbow Six: Vegas ~ Tie
Tom Clancy’s Rainbow Six: Vegas 2 ~ Tie
Tom Clancy’s Splinter Cell: Double Agent ~ 360
Tony Hawk Project 8 ~ 360
Tony Hawk’s Proving Ground ~ 360
Top Spin 3 ~ 360
Transformers: The Game ~ 360
Turning Point ~ Tie
Turok ~ 360
UEFA Euro 2008 ~ Tie
Unreal Tournament 3 ~ PS3
Viking: Battle for Asgard ~ 360
Virtua Fighter 5 ~ 360
Virtua Tennis 3 ~ 360
WWE Smackdown vs Raw 2008 ~ Tie
World Championship Snooker 2007 ~ 360


Summary
Better on 360: 74
Tie: 38
Better on PS3: 10

Methodology

"Key to our quest is mastery of the video outputs of the respective consoles. Zero-compromise 24-bit full-range RGB captures from the HDMI ports of the Xbox 360 and PlayStation 3 allow us to produce the best comparison screen grabs, while Eurogamer's h264-equipped video player means the best in streaming video (make sure you have that 'high quality' feature enabled). And if all that isn't good enough, the high-def captures in all their 720p 60FPS majesty can be downloaded for playback on fast PCs, Xbox 360 or PS3 via the author's blog where similar content for the technically obsessed can also be found. [Enough plugs. - Ed]"


http://www.eurogamer.net/article.php?article_id=318609

There is a more permanent and friendly link now: http://misterslimm.wordpress.com/360-vs-ps3/xbox-360-vs-ps3-head-to-head-face-off-results/

If you could update the first post, that'd be great.

Ones highlighted are the ones i know are wrong. Bioshock was a tie (some things better on one some better on the other)

ps3 version has way better view distance in gta4, and a LOT LESS pop ups.

Soul calibur also looks better on the ps3.. err i don't wanna start a argument and i don't care if you reply to this or whatever, but this list isn't that correct. If you can visibly see faults (take the gta example) then alll your equipment don't mean shit. The equipment usually means that it's something you'd usually not see by eye.