I have had a lot of pets in my life ranging from ant, to fresh water fish, saltwater fish, ferrets, several breeds of dogs, rats, guines pigs, rabbits, Parakeets.
I almost bought a redtail hawk to start doing falconry, and I still might in the future, it just take more dedication then salt water tanks.
I almost bought a Hedgehog one time to.
One of the most unusual I have looked into online was a sugerglider, I can not have another ferret which was one of my favorite pets, and a sugerglider is cool, but if you stray from the proper diet on them, the develop a diesease in thier hind legs.
When I was looking at exotic pets, I was looking for something very unusual like
Fennec fox
http://www.juliesjungle.com/fennecfox.php