Steam are currently running their Halloween special, and boy are there some amazing prices in there. I can only speak for the English version of the sale, but it's difficult to pass on such offers as Ghostbusters for £1.74 and Ghost Master for less than a pound.
Other potentially unmissable titles include Left 4 Dead 1 and 2 for £7.81, Silent Hill Homecoming for a tenner, F3AR for £17.99 and so much more.
It's times like this that I wished Steam would ban my credit card.
On top of most of the above, I'll be picking up all the Overlord games for less than £4 and anything else I can convince my girlfriend is work-related research for an article on the horror genre.
