What tools are available to build unstructured grids for ocean models?
The simplest is triangle http://www.cs.cmu.edu/~quake/triangle.html which is providing lib form many other more advanced packages. You can create poly file and create "holes/islands" in grid etc. Easy to make simple grids.
Another more advanced / gui is xmgredit where you can create/modify grids.
Blue kenue  etc.. 
use the force luke, do a google and it will popup many other packages,
I just wrote a few which are free and for 2D ocean applications.