Hey Lyudmila, welcome to permies :)
I've read about cremini/portabello and it seems like that venture wouldn't pay off very well as the market tends to be a bit saturated. (white button is the most cultivated mushroom after all)
Along with a few others that replied, I'll also be trying to grow morels this year. From what I've read, they have a symbiotic relationship with Elm
Trees (probably a few other trees to) and around here Elms were the pioneer trees planted on all the farmsteads, so I'm hoping I'll get a patch created.
You could try reishi or maitake, as everyone wants to make a tea out of those these days. I'm not certain on the proper way to grow them, but it likely will be similar to shiitake.
Something easily forgotten is that you could sell a different type of oyster. If your market is filled with white oysters, trying growing blue, yellow, pink or king oysters - this makes the assumption you have an indoor setup though. There are usually 3-4 different colour of peppers in stores, all of which sell well. Cooking has a lot to do with colour&presentation and if you are the one offering a product that deviates from the norm, people will come to you so they can cook with produce that stand out.