MGS4 - very good game, the game is heavy on cut scenes but it is enjoyable game overall

ratchet and clank: tools of destruction - very good platformer cum 3rd person shooter, better than LBP imo

the rest have already been rocommended, i just wanted to add those 2 games.

Buy all PS3 games I own !!

Gran Turismo 5 Prologue (Or just wait for GT5)
Haze (I admit, it's not a must have )
InFamous
Killzone 2 (Bit dissapointing SP mode, still nice)
Little Big Planet (Almost not worth it just for SP)
Metal Gear Solid 4
Ratchet & Clank Tools of Destruction (cheap)
Resistance Fall of Men (cheap)
Resistance 2 (Best PS3 shooter IMO)
Uncharted (cheap)
Valkyria Chronicles (worth every cent)

So easy,

KILLZONE 2!

also get Metal Gear Solid 4, and LittleBigPlanet (no, really, you'll love it!)

Maybe get Resistance 2 if you want a bit of run and gun.

Resistance 2( better than the first) , little big planet, killzone 2, uncharted, infamous, ratchet and clank tools of destruction and quest for booty.

Don´t get heavenly sword.

rpgs
Valkyria Chronicles
Disgaea 3
Demon soul and folklore if you like rpg-adventure games
also if you have fallen in love with eternal sonata on the XBOX 360 make a gift to your self and buy the ps3 version new missions,story events,weapons,secret places,characters,items,costumes,upgrated battle system and many more that will make you reach 40 hours of gameplay and if tales of vesperia release in the west go get it i will get bored to tell you all the new stuff i will copy paste from wikipedia

[edit] PlayStation 3 Enhanced Port

PlayStation 3 box art.Tales of Vesperia will be ported to the PlayStation 3 and released on September 17, 2009[13] with additional content as well as a different logo. A PlayStation 3 port has been long rumoured and was finally leaked from the April issue of Shōnen Jump and was officially announced at a Tales Press conference by Namco Bandai on April 6, 2009. It is the second to be released in the Tales Line-Up of 2009, after Tales of VS, an escort title for the PSP, and before Tales of Graces, the new Mothership Title for the Wii. No Western release has been announced. The Tales of Vesperia PS3 demo was released July 13, 2009 in the Japan PSN store.


[edit] Additional Content
Full voice acting
Tie-ins with Tales of Vesperia: The First Strike[14]
New playable character (Patty Fleur)
Flynn as a fully customizable, playable character
Repede and Flynn as selectable on-screen avatars
New cutscenes
New subplots
New main game quests
New sidequests
New songs
New towns
Remodeled towns
New dungeons
New bosses (including the Sword Dancer)
Boss fight replays at Nam Cobanda Isle (in an area called the Door of Memories)
New Overlimit Levels 5 and 6[15]
New Hi Ougi/Mystic Artes (including a dual Mystic Arte with Yuri and Flynn)
New Artes
New Skills
New Equipment
A Key Item known as the "Artes Ball," which allows characters to assign up to 8 Artes to the left stick, and 8 Arte Shortcuts to the right stick for a new maximum of 16 Artes.
New Costumes (Including costumes based on other Tales characters and Sgt. Frog[16])
New Skits
A scene-skip feature
Connectivity with Tales of VS[17]
Pre-Order Bonus (Abyss character costumes for Yuri, Flynn, and Estelle)

as for shooters RESISTANCE 1-2 KILLZONE 2 those 3 are the best on the ps3

Well, personally I would grab:

Killzone 2

Valkyria Chronicles
Disgaea 3

LittleBIGPlanet


That is a great place to start because you get a lot of different stuff and all of them should last pretty long, especially LBP.

Wikipedia has a nice list of all ps3 games. Go there and look at titles that suit your fancy. I am tired of threads like this.

You have the entire internet at your disposal and you come to us about your "what games should I get for X system?"

I thought you were Kowenecki there!

Folklore and Valkyria Chronicles are a Must as exclusives.

Disgaea3
Valkyria Chronicles

If you like SRPG's, these games simply do not disappoint. Especially Disgaea

If you like online Shooters: Killzone2 [I can't think of a better choice]

Action/Adventure fan? Uncharted is a pretty solid game. And the Sequals right around the corner, so you won't have to wait long after playing the first.

Also, inFamous is a great Sandbox Action Game with Third Person Shooter mechanics and a very enjoyable story. It's a really addictive game that's simply a blast to play. I beat it on both good and evil and got all the trophies in about 25 hours. Thing was, I did this in less than 3 days. Just a little more than 2 days actually. One of very few games that made me think sleep simply wasn't important.