"Exotic steel" is either high alloy or just plain hard to find, usually expensive. CPM S30V could be considered exotic because it is high alloy and uses the particle metallurgy process, even though it is has become fairly common (the standard, actually) among high end knives.
If you want to look at really exotic steel, ZDP-189, CPM S90V, and a few other steel types have started to gain popularity. These steel types reach for the limits of what steel can do as far as edge retention is concerned.
They are the focus of most of my collection.
Then you have H-1, the first metal (its not technically steel) to give decent edge retention while being completely rust proof.
And Damascus steel, which is very beautiful. It usually consists of several types of steel folded together to give it an elegant pattern. The Kershaw Damascus Leek is a good example and is very reasonably priced. Most of the time you cant find a Damascus blade for less than $300.
Thats a basic rundown of exotic steel.