Cheap PC preorders. ~£48 for two games.
Zavvi have a coupon “ZAVSEP50” for £5 off when you spend £50. There’s a fair few upcoming PC games that you can use this voucher on to get extra cheap, if you are buying two at once. You have to be a bit strategic with which ones you pick, since some of them are already under £25, and you need to spend a total of £50 or more to be able to use the voucher.
Here are the games that might be of interest to you:
Batman: Arkham City – £21.85
AssRev – £23.85
Driver: San Francisco – £23.85
Aliens: Colonial Marines – £24.85
Rage – £24.85
The Darkness 2 – £24.85
Bioshock: Infinite – £24.85
Tomb Raider: The New One – £24.85
Anno 2070 – £24.85
Xcom – £24.85
Max Payne 3 – £24.85
Borderlands 2 – £26.85
The Elder Scrolls V: Skyrim – £27.85
Saints Row: The Third [Professor Genki’s Hyper Pre-Order Pack Edition] – £28.85
LA Noire – £28.85
DOTA 2 – £28.85
Metro: Last Light – £29.85
Battlefield 3 [Limited Edition] – £29.85
Modern Warfare 3 – £34.85
AssRev [Collector Edition], PC – £39.85
Zavvi is operated by The Hut, and they have a pretty bad track record for customer service. But they’re also cheap.

Does anyone know if they ship separately? For example, if I preorder two games, one for Nov release, one for March 2012 release?
P.
Of course they will ship separately, they would be crazy if they waited for march 2012 to ship them together!
I did seem obvious but then I wonder what happens in the event that you cancel your order after the first ships, or even if the second is cancelled – do you get charged the first minus the fiver discount? (I’m not _really_ concerned about this, just idly curious!)
P.
The discount is applied to both prices (not 2.5 – 2.5 it varies). So if you cancel one of the items, you loose some (or most) of the discount.
Preorder DOTA 2? No thanks. I choose not to pay for a game which will clearly be free to play.
It’ll probably be some collectors edition thing, where you might get a bunch of heroes/skins, similar to how you can buy League of Legends on Steam, quite a bit cheaper than £29 though.