I soak portabellos in a mix of soy and maple syrup for about 30 minutes, then I grill them. So good! I even love making Portabello cheesesteaks when I don't want to eat meat.
The best mushrooms I ever saw were at the food market in SF at the Ferry building. These guys have every kind of fresh mushroom you can think of. Every top chef was walking out with boxes of the most unique mushrooms.