F.E.A.R. Makes a Multiplayer-Combat only game/installer. I think its free or used to be free.
Called F.E.A.R. Combat.

As far as I can tell it was F.E.A.R. with out the single player mode.
Also you can try finding Halo Combat Evolved. Yeah its a 9 year old game. But I still play it on occasion.
Halo 2 requires you to pay-2-play. :\
I also play Unreal 2004.

But these are terrible suggestions for you. I prefer arcade over tactics. I like firing gunzablazin' rather than crouching and hiding behind corners. And all these games arent technically graphics marvel. My RAM is like 1GB so my games are limited.

 

Thanks for the suggestions guys
What do you all think of the tom clancy games (rainbow six vegas 2)?
Thanks!

 

Nexuiz is fun, and fast-paced. Think Quake, but open-sourced with awesome graphics.

 

CrossFire Online is the best FPS for me, its almost like a counter strike game.

 

Rainbow Six series of games, Armed Assault 2, Operation Flashpoint: Dragon Rising. A few tactical type shooters you may be interested in. I preferred some of the older Rainbow Six games compared to the newer ones. It just seems they got a bit less tactical and more -arcadey-.

 

Counter Strike Source, Best fps I have ever played, I've got around 400hours logged on to that game

 

Team.

Fortress.

2.

 

You have a 5 year old midrange card, I doubt any game will look good on your computer.

 

Unreal series.. UT 1 is my fav but very old

I also like Deus Ex.. not a real FPS like Unreal and COD but still a FPS and soon DX3 is coming yay

Half Life series ofcourse
SW Battlefront
CS:Source
STALKER series
FEAR series
Crysis
Far Cry series
ArmA 2
Doom series.. plain classic

Theres loads of other good ones but not really FPS more like 3rd person action games