Looking for a new FPS...

[#1]

I'm a big gamer on the 360 and love FPS as stated above COD3 is an excellent online game holding 25 persons per room.  Rainbow Vegas was also a big game, but I have now gone off this game as there still seems to be many bugs which in my view ruins the game play, most of the people i'm online with no longer play this.
The best title out is GRAW2 this is a fantastic online experience.. with many different game modes.
Blind seige is one of the best out there, following on from the Ghost Recon past games.  well worth a purchase.

[#2]

CounterStrike is awesome.
BF2 and BF2142 are great too, there are plenty of mods out there for BF2, I am currently playing PR Mod (Project Reality) very good realism.
CounterStrike also has a good mod called Insurgency,which is still beta, but i must say its a damn good beta.
I recently picked up COD2 and since playing that, i thought i would install good old Medal of Honour again not played MOH series for a while.
Also there is alot of hype about Quake Wars (due in September), i didn't get the chance to play the beta, but have been told its going to a very good.

[#3]

An oldy that I play in tournamant is Joint Ops...IC mod....250 player servers...battle days are a scream, and the public servers are always busy.  Plus you can get the whole game and expansion pack for next to nothing... the IC mod is free.  Try it.
Also the ultimate realistic FPS I now play is Armed Assualt, need a fairly decent Pc though

[#4]

I know it didn't get stunning reviews but if you're after a cheap Xbox 360 FPS, then I also enjoyed Prey quite a lot.
It is admitted quite short (maybe 6-10 hrs-ish) but it has some really good touches and ideas that I hope will be expanded upon if a sequel emerges - portals, experiments with scale, techno-organic weaponry, spirit walking etc. It's a nice looking game, I found the story to be interesting and it's pretty atmospheric at times (it has a few stand out moments).
The multiplayer is poor though, very laggy from my experience and lacking a lot of people playing it. Maybe the PC version is better in that respect.
That said, if you're after a quick, cheap blast for a couple of play throughs on single player, then you could do worse.

[#5]

I agree with Beetroot Bertie, Pray is a very nice looking FPS on an average spec. PC (it uses the Doom3 engine), with an involving story which pulls you along. Don't buy it for the multi player option, it's very limited. But hay, it only cost me a fiver from Play.com, so it's very good VFM, I'd say, if you can get it for a tenner or less.
A must have game has to be HL2, along with BF2 (a tenner from DVD.co.uk), but the spoiler for BF2 is the loading/wait times between games of around 5 minutes. Don't get BF2142, unless you like having adware  installed on your PC.

[#6]

Try FEAR Extraction point the expansion 
Its explains more of the story and scared the hell outa me 

[#7]

try the darkness thats a good one on 360, also try gears of war is more 3rd person but great fun and violent ^^

[#8]

I am not sure you can count this as a FPS because you use your own powers as opposed to firearms...
But City of Heroes MMOL is brilliant. you can download a two week trial for nowt.
Be aware though it is a  2gig download
http://www.cityofheroes.com/promos/covpreorder.html

[#9]

i still play BF1942 loads, the amount and variaty of mods for it is amazing. If you prefer something more up to date there's BF2, not quite so good but there's plenty of mods in the works for it.

[#10]

I'd highly recommend both PREY and S.T.A.L.K.E.R  as the two of the best single player FPS. 
Both suck for multiplayer though. COD2 is still tops for me in that category.

[#11]

The soon to be released Bioshock should be a good FPS to get into too.
I've downloaded the demo from Xbox live and it's very impressive indeed. Great art style and atmosphere. And wonderful use of sound and music to set the scene too.

[#12]

If your PC is upto it look out for the release of CRYSIS and FAR CRY 2 both look awsome. 
http://farcry.uk.ubi.com/newsarchives.php
http://www.electronicarts.co.uk/games/8456/

[#13]

There's not been much input from the author of this thread -when I say not much, I mean none-, come on we are all coming up with some classic FPS title suggestions here
Oh yeah, I played the demo of Bioshock. It's sort of an under water Doom3 in an Art Deco style, with a lot more interaction with the environment; good, but not quite a classic from what I've seen.

[#14]

I love Day of Defeat Source. Try it. It's nice

[#15]

BioShock - awesome awesome awesome