[raptrex]

How do you find it if you do have a vanity URL?

[far33d]

http://graph.facebook.com/<user_id>;

[harryh]

View source on your profile page and search for profile.php?id=

Right after that will be your id.

(There are other ways as well, but this is a pretty easy way)

[whakojacko]

as linked below, http://www.rabidgremlin.com/fbprivacy/ will give your FB id.