Terrain map generator with JavaScript and HTML5/CSS
That map looks super cool! The performance isn't THAT bad, considering you're generating 2500 DIV elements :) 

What you could do is generate one Canvas instead of so many DIVS. The GPU can render a canvas super-fast. That will also be helpful if you start adding more elements to your game. 

There is no reason to use jQuery, so you can get rid of that too :)