Aperture question - Plugins

Hello everyone,
Well to all Aperture users, I have been wondering....what are the must have free plugins? and what are the must have plugins? I just wondering.

And it would be great if someone would tell me how to install these plugins

P.S: Is there any free Aperture plugins that allow you to add some sort of white transparent custom made signature on the bottom right of the picture when you export the pic or any similar?

thanks jalagl, I will try to do it cause I got a rough idea how I want my watermark design to be in it. Somehow I dont trust the upload to the internet without watermark stuff cause eventhough it wont be as quality as the original, people could still take your stuff and post it in blogs or edit it into their blog design or something and I bet you cant do anything to them eventhough you posted copyright in flickr......