According to this site:

http://www.thesixthaxis.com/2009/07/10/ps3-to-pick-up-360-title/

Exclusive: PS3 To Pick Up 360 Title
By Alex C [nofi]

Whilst we can’t reveal any specifics right now, we can now reveal that the PlayStation 3 will play host to a popular 360 favourite.  The title, which has to remain under wraps with us for the time being, will be released towards the end of the year.  We’ve been promised more information in roughly a month’s time, at which point we’ll be able to share the specifics, first.

Our contact has also let us know that the studio will have other exciting news to share soon enough.  Note that we can not talk about this further at this stage.

Have a good weekend.

- I think its mass effect, just because recently bioware said how they were excited on developing on the ps3

Doubt its Mass Effect because they said "towards the end of the year".

My guess is either L4D2 ("step-child version")
or
Splinter Cell: Conviction

Other than that... no idea

Well it saying that a 360 favorite which has already been released is releasing later this year on ps3, im really sure its mass effect, then mass effect 2 releasing early next year for the 360 and ps3 would make perfect sense.

Maybe Gears of War

Tales Of Versperia US version ?
or do they mean unannounced ?

thesixthaxis, I've read some of their reviews, but how much credibility do they have as a news site?

ALREADY been released... ahh.

I thought it meant the game wil lbe releasing towards the end of the year.

In that case, no idea.

Gears or Mass Effect or Left 4 Dead or Halo 3

Who says it was a disc release. Maybe arcade game

All signs point to L4D.

ME 2 is not coming out this year.

Halo 3? There is no way halo 3 can release on the PS3

Left 4 dead is a possibility, so is Mass effect, but not gears of war