It can come with whatever top.  Black Delrin I think is the best overall material for waterblock tops.  Even when I use polycarbonate (lexan aka "bullet proof glass") tops, the material can still crack, but its much better then plain jane acrylic. 
 
So here is a picture of what the block will look like on the board, from the top down in CAD:

 

Sorry for being way off topic, but would you be willing to make me a waterblock for my 590? I would pay you of course.

I try to do batch type of work, its easier. It takes quite a bit of work designing and prototyping so its easier to spread the costs of that amongst more people

Aww I see, thanks anyway man.

No worries.

I think we have a veteran forum member donating a board for the effort! More to follow

UPDATE:
A member donated their board to the cause. Thanks Boatswain!

That's awesome news.

Yes, its great news. While having 3d models help, there is no substitute for the real thing. I have the first chunk of copper ordered. I will bang out an aluminum prototype, calculate some rough pricing, and start seeing who is seriously interested.

I'm definitely interested. So when you get the pricing straight, just shoot me a pm and we'll go from there.

I'm in nateman, I would like a nickle plated one though, either you could organize it
or I can get it done once I receive it (I know a good plater here).
Hope you don't mind posting to Australia ;)