Hi, im mostly a PS3 and handheld gamer, but during work i now play PC games at lunch times, just finished the first Mass effect as it wasnt on PS3 and now playing oblivion as the PS3 version doesnt have trophies. 

But looking around on steam im already finding it hard to find games that ive not already got on PS3 to play. So could you reccomend me some PC exclusives that you think are great. 

Half Life 2 :P You can get it very cheap on steam and its awesome ;D

what genres you looking for?

Since you liked the original Mass Effect, you should definitely get Mass Effect 2. It stands up as my favourite PC game of the last couple of years.

EDIT: It's not a PC exclusive, but it will be much better on PC if you can import your ME1 save data.

A couple other questions, will you be playing any online multiplayer or are you looking for exclusively singleplayer games, Also how important are graphics to you any eversion to PS1 level graphics lol? Oh and would that be action or point and click adventure?

As for some stock reccomendations off the top of my head Mount & Blade: warband, Magicka, try some Spiderwebsoftware RPGs they have big demos, Starcraft 2, the Witcher, Total War series and the S.T.A.L.K.E.R. series 

As always read some reviews and when possible try some demos before buying is always advisable

Im more of a single player gamer, but not adverse to online games, also im not that bothered about graphics. For adventure games i guess i mean action like Uncharted and Ass Creed and the like, ive done my fair share of point and clicks in the past, struggle to get away with them these days, got sam and max season 2 free on PSN but the dialogue just dont seem as funny as it did back in the day.

Id forgotton about starcraft 2 with it not being on steam so ill definatley look into that, and the witcher looks interesting.

Unfortunatley i played ME2 on PS3 first lol, then decided to play ME1 afterwards just to re live my interactive comic choices :)

I was quite surprised how differnt the 2 games were in terms of game mechanics, they made alot of changes, i think 2 is still my favourite, even tho 1 felt more epic.

Any of the Total War series should scratch your strategy itch, as well as the more hardcore Pardox titles like Europa Universalis and Victoria 2. There are also a ton of RTSes, like the Dawn of War series, Company of Heroes, World in Conflict etc etc.

For RPGs all of the old Infinity Engine games like Baldur's Gate, Planescape, Icewind Dale etc are available for cheap on gog.com- there's a ton of mods for them as well which make them more better-looking and more enjoyable to play. Neverwinter Nights 2 recently appeared on Steam, but it's been on sale a couple of times, so might be worth waiting on that one. Also look out for some newer excellent European RPGs such as Drakensang, Risen, The Witcher and Divinity 2 as well as real old school indie ones like the Eschalon and GeneForge series.

Not exclusives, but the PC versions of Left 4 Dead and its sequel and Team Fortress 2 are light years ahead of the console versions. Other good exclusive shooters include STALKER, Killing Floor, Arma 2, Red Orchestra, Crysis and Amnesia (not really a shooter, but pantwettingly scary and has just received a free extra campaign).

Civ IV >>> Civ V. You should really try it despite owning Civ V already. There's a demo available in case you're interested.

Total War series if you care for strategy games. Rome is possibly the best game in the series, but the recently released Shogun 2 is also one of the better games. There's a demo for at least Shogun 2.

The first Crysis is pretty awesome. You won't find a great story there but you'll find a great shooter with open environments and quite much freedom in what you do. Also, the nano suit is pretty fun.

I recommend trying Enemy Territory: Quake Wars if you care for multiplayer. It's not exactly exclusive but the PC version is far superior and the console versions never got that popular I think. The PC version doesn't have a huge player base either but you should never have trouble finding a server with enough players on it. Or you can try the free Wolfenstein: Enemy Territory which, while quite old already, is still very much alive and great. They're quite similar but they do have some differences as well.

Titan Quest is a Diablo clone. Some hate it, some love it. Personally I find it great, and there's a demo available. Of course Diablo II is still alive and shouldn't cost that much either...

Supreme Commander is definitely worth trying if you like strategy games. Huuuge scale battles, all in real-time. There's a demo for the game.

Deus Ex is already quite old but you should definitely try it. There's a PS2 version but... If you haven't played it, you should really try out the PC version. No, seriously. Try it. There's a reason why its has such good reputation.

Another must-try classic is Baldur's Gate II. You've probably heard of it and if you haven't, you should be ashamed. There's a demo for this one, too. The first game is pretty good too but BG2 is what you should try if you want something truly awesome.

Some other classic RPGs would be Planescape: Torment, the first Fallout games, Arcanum, and if you like combat in Baldur's Gate II, the Icewind Dale series might be good for you.

Then there's tons of adventure games. I don't really have much experience with them (I really don't have enough time for all the games I own), but The Longest Journey is supposedly quite good and decent-looking even now.

Operation Flashpoint is a must-try if you like war games/shooters. It's quite realistic but it's not that hard to get into if you dive into it with an open mind.

In case you like city building, I have a recommendation. Well, an old game but anyway. Emperor: Rise of the Middle Kingdom is quite fun. It's set in China from its foundation to the 17th century or so.  It's in the same series as Zeus and Pharaoh and such.

Yeah, I think that's pretty much it. There's probably tons of games I missed but there should be something for you here - probably for a longer while too. Have fun with your choice(s)!