Well, we didn't know what he wanted it for until he mentioned pCARS. I was going to get Arkham City for £1 on OnLive a while ago but I couldn't get my account to log in so I gave up and haven't tried since, my computer is fine so Steam is still my personal service of choice. People with computers not up to the task of DX11 and not enough money to build a new one would probably get a lot more out of OnLive than people like me... Being unable to play online games is better than being unable to play games full stop, after all!
Edit: also, to the OP, I suggest saving up roughly £500 or so. Get an i5 as close to 3GHz as possible, a suitable motherboard, a PSU which would power a DX11 graphics card and a cheap 512MB-1GB graphics card, 4GB RAM then the biggest hard drive you can afford (don't even begin to consider an SSD!). Don't sell your wheel (I really don't understand why you want to do that and then buy a PC for pCARS) and play rFactor, Simbin titles, Richard Burns Rally and GP Legends until pCARS is released properly, then swap the graphics card and hope your processor is good enough, really... 3GHz should be fine, though, but a 2500K unlocked 3.3GHz CPU would be perfect, some say it's all you'll need for this generation of gaming and it's very popular for gaming rigs but you do get the occasional person telling you you need an i7, but you don't. An i3 is too little, though, and you'd definitely need to upgrade it soon.
£500 is a rough estimate based on my PC costing £1,100 with an i5 2500K, GTX 580, 850W PSU and a 128GB SSD, so if you save a lot on the graphics card, don't buy an SSD at all, go for something below an i5 2500K and get a 650-700W PSU instead I imagine you can still get something pretty good for £500.
Edit again:
nitrorocks
Also, don't forget iRacing and Sim raceway.
No, absolutely do forget all about iRacing, it's incredibly expensive; the monthly subscription is the cheap part because cars and circuits beyond the handful they give you are £10 each (I think) and you're limited to what they give you to choose from. rFactor is completely the opposite because everything is free and there are some truly excellent mods; Touring Car Legends, AE86 Club, DRM Revival, Enduracers, Z Cars, Historic Rally Cars and Group B Rallycross are just a few that add a huge amount of cars, many of which you won't have seen in anything on the PS3 or indeed real life, quite possibly. I had no idea DRM machines ever existed, they're basically what Group B circuit machines would've been if the F40 and 959 weren't the only two in existence.
I write a lot, I'll stop now.