I always found Rocks to be a great addition to a table. Massive boulders being my favourite as they not only block movement but also line of sight. With that In mind I set about getting a test piece done for my own board:
This piece turned out really well and I am half in the mood to make a themed set of terrain that pretty much is only out crops like this. I can imagine it would really make for some interesting decisions when traversing the board. They are really simple to make, just some cork chunks on a cd with some cheap modelling clay to blend them into the base a little better. Painting them is simple!