Depending on where you live, there are many late summer bloomers: goldenrod, purple coneflower, black-eyed Susan, Queen Anne's lace and, one of my favorites, purple asters.
Yes. They basically bloom from August 5th through September 5th. It might be tempting to transplant them and add them to your garden, but varieties such as the Purple Fringed Orchid or the Indian Pipe will die if you move them due to their need to live off a certain fungus. Check with plant guides for further information.
Many wildflowers bloom during the august month. Of course it depends on where you live as to what blooms. The summer sun and extra rain of august usually help with more blooming.