I looked around quite a bit, but just this weekend sprung for one of those chessex wet-erase jobs.   It's a little over 2 feet by 2 feet, I got the 1 inch squares marked one, but they make double sided (with hexes and squares), and also much bigger ones.  It's thick and sturdy, I have a couple friends who have owned one for a year or more and neither show signs of wearing out, and the one I got was about 14 dollars.  Totally worth it.