If you already have an Xbox360...then I doubt you really need to get the PS3 since most third party games will be on both PS3 and Xbox360...
and here's the list that will be on
both PS3 and Xbox360.
Cipher Complex -2007
Dark Sector-2007
Heavy Rain-2008
The Club-2007
Frontlines: Fuel of War-2007
Stranglehold-late 2006
Turok game-2007
Golden Axe game-2007
Army of Two-2007
Resident Evil 5-2007
the next King of Fighters: Maxium Impact-unknown
Killing Day-late 2006
The Darkness-2007
King Kong-late 2006
Pirates of the Carribbean game-2007
Alone in the dark-2007
Avalon-unknown
Brothers in arms : hells highway-2007
Call of Duty 3-late 2006
Dirty Harry-unknown
Fight night round 3-already out for Xbox360, unknown for PS3
Grand Theft Auto 4-2007
Half-Life 2-late 2006
Heat-2007
Haze-2007
Hellboy-2007
Indiana Jones -2007
Marvel: Ultimate Alliance-late 2006
Madden football-2006 to 2007 (sports freaks: all sports games including football and basketball will be on both PS3 and Xbox360)
Medal of Honor: airborne-2007
Possession -2007
Project Delta -unknown
Rayman 4-late 2006
Sonic Adventure 3-late 2006
Spider-man 3-2007
more star wars games to come around 2007 for PS3 and Xbox360.
Sega Rally Revo -2007
Stuntman 2-late 2006 or 2007
Schwarzenberg-unknown
Tom Clancy's Splinter Cell Double Agent -late 2006
Tony Hawk's project 8-late 2006
Tom Clancy's Rainbow Six Vegas -late 2006
Transformers-2007
The Wheelman -2007
The Outsider -unknown
Ubisoft's Teenage Mutant Ninja Turtles game -2007
Virtua Tennis 3-2007
SmackDown! vs. RAW 2007-late 2006
...and so much more.
Still, if you already own an Xbox360, I feel there's really no point to get the PS3 when alot of games would still go to the Xbox360 also.
psst...even Mercenaries 2 would still go to Xbox360 also.

They DID say it's a possiblity for that to happen, so...
What? dont believe me? then here's the quote:
"Pandemic recently announced that Mercenaries 2, originally thought to be a PS3 exclusive will also be released for the Xbox 360. The Xbox 360 version will be released in October and feature slightly better graphics and the PS3 one will be a launch title."
If you already own an Xbox360, you are already good enough.