Blizzard releases Wrath of the Lich King system specs

And they're not so heavy, which is nice. Here you are:

PC System Requirements

OS: Windows XP (Service Pack 3), Windows Vista (Service Pack 1)

Processor:

• Minimum: Intel Pentium 4 1.3 GHz or AMD Athlon XP 1500+
• Recommended: Dual-core processor, such as the Intel Pentium D or AMD Athlon 64 X2

Memory:

• Minimum: 512 MB RAM (1GB for Vista users)
• Recommended: 1 GB RAM (2 GB for Vista users)

Video:

• Minimum: 3D graphics processor with Hardware Transform and Lighting with 32 MB VRAM
  Such as an ATI Radeon 7200 or NVIDIA GeForce 2 class card or better
• Recommended: 3D graphics processor with Vertex and Pixel Shader capability with 128 MB VRAM
  Such as an ATI Radeon X1600 or NVIDIA GeForce 7600 GT class card or better

Sound: DirectX-compatible sound card or motherboard sound capability

There's more on the Blizzard forums, including Mac specs.