HALF-LIFE 2: THE ORANGE BOX for the PC - £14.99 Delivered, or £14.69 with attached voucher.
Don't forget you can also get cashback on top of this (e.g. 4% from Quidco).
Games included are:
Half Life 2: Episode One
Half Life 2: Episode Two
Team Fortress 2
If you haven't bought it yet, you should - these are some of the best games ever made, and all in one package. :)