I agree with several of the comments already made. To me a rat-bike is much more than just a bike missing some parts. I also don't think a rat-bike is a bike with a bunch of random crap glued on. There is a very fine art that includes hand crafted parts, proper amount of a "patina" and/or raw metal, and certain attitude which may not be possible to put into words. So here are a few examples of what I'd consider to be nice rats, starting with my own CHOPPRD Rd400...
I think just about all of the bike you see each year at the Dirtbag Challenge fit the category nicely... especially these two bikes built by the Turk...
A few others from the DBC...
and I think some of the choppers from AfterHours Bikes are quite nice examples of the rat look...
Anyway, those are a few rat-bikes that come to my mind.