2K Games and Firaxis are now offering pre-sales of XCOM: Enemy Unknown, their upcoming continuation of the strategic elements of the XCOM series of counter-UFO games. This is available through various digital distributors and includes the incentive of the Elite Soldier pack, which offers "top-of-the-line soldier customization features" they say "will only be available while supplies last" (which, as usual, begs the question of how you exhaust a supply of digital content). They also announce that those who pre-purchase the game through Steam have the opportunity to unlock incentives based on the number of other preorders: "If enough people pre-order XCOM: Enemy Unknown , they will unlock 3 exclusive XCOM-themed items in Team Fortress 2. If even more people pre-order, they will unlock a free copy of Firaxis’s other big title, Civilization V (and yes, you can gift it to a friend if you already own it)." Finally, with about a month to go before the game's release, they provide us with its system requirements:

Minimum Requirements:
OS: Windows Vista
Software: Steam Client
Processor: 2 GHz Dual Core
Memory: 2 GB RAM
Hard Drive: 20 GB free
Video Memory: 256 MB
Video Card: NVIDIA GeForce 8600 GT / ATI Radeon HD 2600 XT or greater
Sound Card: DirectX Compatible

Recommended Requirements:
OS: Windows 7
Processor: 2 GHz Dual Core (Intel Core 2 Duo 2.4 GHz or Athlon X2 2.7 GHz)
Memory: 4 GB RAM
Hard Drive: 20 GB free
Video Memory: 512+ MB
Video Card: NVIDIA GeForce 9000 series / ATI Radeon HD 3000 series or greater
Sound Card: DirectX Compatible

Additionally, VG247 has posted an E3 Gameplay Walkthrough video from the game.