Here is a helpful template from DreamGrow correct as at October 2011 with the dimensions for the different elements on Facebook:

Profile Picture For Facebook Pages

Width: 180px
Height: 540px

Facebook Page Avatar - displayed against every post

Width: 90px
Height: 90px

Facebook Landing Page

Width: 520px
Height: Unlimited

Maximum Size Of Pictures That Can Be Uploaded

Width: 2048px
Height: 2048px

Maximum Size Of A Picture As Displayed

Width: 960px
Height: 720px
Facebook ads

Facebook Adverts

Picture width: 110px and height: 80px
Size: 5MB

Header: 25 characters
Body copy: 135 characters

Facebook Status Update

Status update length: 63,206 characters
Comment length: unlimited

Video

The maximum size of vide you can upload is 1024MB and a length of 20 minutes

And a bonus tip for your personal presence on Facebook:

Facebook Profile Timeline Image

Width: 851px
Height: 315px