Donald Trump's inauguration just got a lot more lit -- Michael Flatley's been booked for the dance floor ... TMZ has learned. The "Lord of the Dance" creator and his Irish dance troupe are the latest act to be added to Friday night's Liberty Ball lineup ... according to our Inaugural Committee sources. We're told they've been wanting to book him for a while, and finally confirmed on Wednesday. Flatley's crew joins entertainers such as Sam Moore at the balls. Of course, The Rockettes will also be there. Not that it's a competition.