I tried to quickly search and reference the Facebook Timeline banner size but nothing came up. Also if you want to save a little bit of time, we have created a quick template for you to use. It includes guidelines and a mockup of where your avatar would exist (this will help accommodate for the design).
The size for the Facebook Timeline banner (or cover as they call it) is 851 x 314 pixels.
Note: We've updated the PSD to accomodate the larger profile photo, click below to go to the post.