The Witcher Enhanced Edition - Directors Cut = £3.49 at gamefly (http://www.gamefly.co.uk/Download-The-Witcher-Enhanced-Edition-Director's-Cut-UK/5001291/)
I loved the game even though it did not do so well.^^I'd second the Chaser recommendation, it is a BIG game (over 30 levels) with a wide variety of environments and weapons. Obviously as a pre-2004 (FC/D3/HL2) game the visuals aren't anything to write home about but if you like your FPS then worth a punt.
Just Cause 2 - £2.49 at http://www.getgamesgo.com/product/just-cause-2
I bought this and it sent me an email with an empty Activation code box. Anyone else experience this?

It is worth it for the Napoleonic addon. 100 v 100 musket action.
Just bought it and the feel of 100 vs 100 is freaking awesome. Literally about 70 dudes lining up unloading the muskets at the enemy at the same time was freaking epic!

battlefield 3 premium £36 using 10% off code on greenman gaming site
http://www.greenmangaming.com/s/gb/en/pc/promo/10-per-cent-off-all-titles/?lower
Gamersgate is having a Magicka collection sale too.
£2.25
Don't know if its steam complient tho, so depends how fussy you are.
Also use quidco and get an extra 6% off, brings this down to £33.83.
Took the Arkham City £4.99 deal from Gamefly as it seemed too good to miss, downloaded the whole 17GB which took forever on my crappy connection. Attempted install, installation stalled at approx 2/3rds and failed to resume! looks like the files are corrupted and i'll have to download the whole lot again, I've never had this problem with corrupted files with Steam or Origin!
Is it worth buying the collection over say, Warband alone?
Only really interested in the single player element of this