I use them to make mushroom gravy - usually I use potato water to thicken and add sauteed fresh mushrooms in with the dried, plus a splash of soy sauce or red wine - the dried give it a deeper, earthier flavor. I've found if you have extra gravy it keeps a long time in fridge and also freezes well. We LOVE love love it with shepherd's pie, and even my non-veg DH prefers my veg mushroom gravy to meat gravy on his potatoes.
Another fabulous use is in mushroom risotto! Again, a mix of mushrooms is our favorite (either fresh + dried, or a mix of dried, like some shiitake plus some other variety). Just chop the mushrooms and saute in a little olive oil with some onion and the rice, and add the soaking water to your veggie broth to be added as the rice cooks. We like to stir in a little red wine at the end, and finish with some fresh chopped parsley scattered over the top...YUM!