So what are some of the best first person/third person shooters that you've ever played that had a multiplayer cooperative mode?

And by "shooters" I am including tactical stuff like Swat 4 and ArmA.

Here is my top 10,

1. Left 4 Dead series
2. Portal 2
3. Dead Island
4. Borderlands series
5. Rainbow Six 3: Raven Shield
6. Ghost Recon
7. Hidden & Dangerous series
8. ArmA series
9. Operation Flashpoint series
10. Rainbow Six: Rogue Spear

I think the L4D series gave me my most rewarding experience.
Of course you always get the odd idiot who goes off on his own but we all know what happens to them

With a good team I found that game unbeatable for an on-line co-op shooter.
In fact when you lost someone,especially on the ending levels I really felt for them.
The number of times I must have died trying to save someone,well I thought I was a hero,albeit a dead one.

In no particular order:

Arma series
DayZ mod (based on Arma 2)
Left for Dead series
Rainbow Six series
Ghost Recon series
SWAT 4
Borderlands series
HALO series
Gears of War series
Joint Operations - Combined Arms

Delta Force, in various incarnations, I used to play a lot of HtH
Ghost Recon played it a lot online with friends in co-op mode
Tried the current itteration of Battlefield but meh.

I would say Ghost Recon with the two addons plus all the community stuff, and the Joint Operations series.

Me and some old friends have had one or two LAN meets each year since way back, but these days we can't really find any good coop games to get in to anymore.
We have tried Arma a couple of times, but the guys just find it too, I don't know, clunky, and we never had as much fun with it as we had with good old Ghost Recon.
And most of the new games with coop has this stupid 4 player limit, I suppose it's some console curse or such..?
Anyway, it's not much fun when there is 8-9 people at the LAN meet, so I guess I will keep an eye on this thread, maybe some good ones will pop up.

Joint Ops is the only one I have extensive experience (but not extensive skillz ) with. I have ArmA and Ghost Recon but never really played them very much. I guess gaming just isn't on my radar right now.

I can't remember, did you play with the SimHQ group back when Joint Ops was really popular? Myself, Jedi Master, Positive G, Paul Morrison and adlabs were among the regulars.

I buy games with co-op in them and always plan to play it but never do, except for L4D 1 and 2 but that just finds games with random people.

At least in L4D the gameplay mechanics 'force' the players to work together or suffer as a result.
If I end up with 3 goons I just find another game.Although,sometimes I am the 'goon'

Yeah, usually the player who goes "lone wolf" ends up getting pounced by a hunter or grabbed by a smoker and that's all she wrote!

Team Fortress 2

Hidden & Dangerous (only played the first one, but it was great. Very challenging though)
Killing Floor (simple but fun shooter when you play with people you know. Don't bother playing with random people though)
SWAT 4 (If played with people who don't get angry easily)
Delta Force series (A tad bit on the simplistic side for what they are, and the ones I've played also got too easy in co-op, but still a fun way to spend an evening or two)