You got any good suggestions besides Resistance 2? I pretty much own every platform except Xboxes.
Resistance 2 is a PS3 game.
Here is the great list (from worst to best)
8. Killzone 3 (PS3) - Totally chaotic shooter! Story co-op game. Play from start to finish with a friend! However the title is misleading! There is not much gore, just big blood splat effects. The enemies can't get limbs or heads ripped off or anything, and it has a surprisingly strong story.
7. Resistance: Fall of Man (PS3) - Campaign from start to finish with co-op, but the strong horror theme could turn you off (It's not that scary though. Imagine a game less scary than the Uncharted submarine base, but still kinda scary)
6. Ratchet & Clank: Full Frontal Assault (PS3) - It's the same game, but a gazillion times funner when you have a buddy to rely on… and yes, I am reliable! (normally)
5. Resistance 3 (PS3) - If you like FPS games, and story mode, then this whole game can be played with a friend from start to finish. It's really cool. And the visuals are stunning, but when it's done it's done. There is no point in playing it again.
4. Portal 2 (PS3) - You got a brain? Does it work? Good, then team up with someone and play this game. This deserves all the popularity it gets. It's super funny, and super fun. When played with a friend it gets even better… just make sure you trust them…
3. Ratchet & Clank: All 4 One (PS3) - Ratchet & Clank, with friends is beatable by only two other games.
2. Resistance 2 (PS3) - If you like shooters, this is the most fun Co-op shooting experience you'll ever find. Play with friends, blast hordes of bad guys, and experience the funnest co-op shooting ever!
1. LittleBigPlanet (1/2) (PS3) - Play, Create, Share. Play dozens of wicked story levels with up to 3 friends (local or online) and customize your character to look any way you want! Ratchet, Clank, Jak, Daxter, Cole? If you can think of a character you can make that character! You can create your own levels too! And submit them to the world to play, you can also play millions of other peoples creations. There is something for everyone. RPGs, Platformers (mostly), Shooters. And create mode is ultra fun with friends! This is a must-play online game!
Well other than Resistance I'd suggest:
Crysis 2 (PS3). You can't play campaign multiplayer but there are more tactics involved compared to other FPS' as you can use the stealth or armour functions of the suit. These make the multiplayer even more confusing and interesting but still great fun.
Star Wars: Battlefront 2 (PS2 or PC). I have no idea whether the multiplayer servers are still running on this. It had a nice campaign where you play both sides and the multiplayer was brilliant. I hope they bring out a new one of these, or a HD release. 
LEGO games (PS3). These are great splitscreen games and completely daft. Try Star Wars or Lord of the Rings.
As RatchetRuler says, definately Little Big Planet.
I just realized something… this is going way off topic.
We should continue this via PMs or a dedicated forum for recommending games.
Are there even any Moderators left? There's like no one here. I remember the old days when this place was swarming with life… ah those were the days.
Oh, well it doesn't matter how many people are here, at least there are people here.
How about the easy way?
http://en.ratchet-galaxy.com/thread-3553-1.php#262360
This was harder than I thought it would be, heres my list:
1. Resistance 2
2. Resistance 3
3. Ratchet & Clank Tools of Destruction
4. InFamous 2
5. Ratchet & Clank A Crack in Time
6. Ratchet & Clank Full Frontal Assualt
7. InFamous
8. Ratchet & Clank 1
9. Resistance Fall of Man
10. Mass Effect 2
11. Mass Effect 3
12. Assasin Creed 2, Brotherhood and/or Revelations (each scored equally IMO)
13. Destroy all Humans 1&2
14. Red Faction Guerilla
15. Jak 3
16. Jak & Daxter The Precursor Legacy
17. Ratchet Gladiator
18. Ratchet & Clank 3
19. Ratchet & Clank 2
20. Jak 2
The Dead Space games, Portal 2 and Pixeljunk Shooter 1&2 are also worth mentioning 
It's not in order…
- Uncharted 2
- Uncharted 3
- Ratchet & Clank 1
- Ratchet & Clank 2
- Ratchet & Clank 3
- Ratchet: Gladiator
- R&C: Tools of Destruction
- R&C A Crack in Time
- God of War 3
- inFAMOUS
- inFAMOUS 2
- inFAMOUS: Festival of Blood
This are my 12 favorite games…
I dont have a top 20,but heres my top 10:
10. Ratchet & Clank 2 (PS2)
9. Zelda Twilight Sword (Wii)
8. Metal Gear Solid 3: Snake Eater (PS2)
7. Assasins Creed (PS2)
6. Call of Duty: Modern Warfare 2 (PS3)
5. GTA V (PS3)
4. Resistance 3 (PS3)
3. Ratchet & Clank: Quest for Booty (PS3)
2. Ratchet & Clank: A Crack in Time (PS3)
1. Ratchet & Clank 3: Up Your Arsenal (PS2)
