Basically what are the top bosses THAT YOU HAVE ENCOUNTERED that are "creative" looking and/or why they interest you. You can have a max of 5 bosses and you may add pictures if you would like. I'll start by giving an example (mind you no real order of creativity just overall creativeness):

1.) Zalera (Esper): Final Fantasy XII - immune to all elements and can instantly kill any Esper summoned as well as the person that summoned the Esper. Must be defeated in 5 minutes.

2.) Dark Yojimbo (Aeon): Final Fantasy X - Do I even need to say anything...

3.) Spiderdemon: Doom - A brain attached to mechanical legs... GENIUS!! The only attack... shooting off it's 50 cal attached to it's body. If you want to die just stand there, you won't have to wait long...
4.) Tyrannosatan: Deathsmiles - The final boss and one of the most difficult that I've seen on a side scrolling game. When you think Tyranno you think Tyrannosaurus Rex... honestly I would laugh if you said he looks just like one. He's not even close to that. He just a unique looking boss. Some attacks literally fill up the screen with you trying to dodge every little bit of them.

5.) Gary Smith: Bully / Bully (Scholarship Edition) - Basically the first "Friend" you make in the game turns out to be your main enemy and final boss. The moves he can inflict are unique in the idea that nobody else in the game can do them. Although if I remember correctly Jimmy and Gary have a move or two that are the same.