I'll second Lynn's Paradise Cafe-funky and unique.
http://www.lynnsparadisecafe.com/
As a PP mentioned, the science center (And IMAX theatre) are a lot of fun and a good way to spend a day
http://www.louisvillescience.org/
The Patton Museum is not actually in Louisville, but is about 45 minutes away in Fort Knox. In Louisville, there is a cool museum that features local history as well as weaponry from the distant past (Culloden, anyone?)
http://www.fraziermuseum.org/
Along with the Belle of Louisville, there is another, smaller steamboat, the Spirit of Jefferson. If one's not available during your visit, the other may be.
http://belleoflouisville.org/aboutus/?pageid=ourvessels
We have always enjoyed trips to the planetarium, located on the campus of the University of Louisville (a side note -GO CARDS!).
http://louisville.edu/planetarium
Venturing outside of Louisville (Within an hours drive) I suggest My Old Kentucky Home, in historic Bardstown,Ky. It's an interesting home, where Stephan Foster visited and it may have been the inspiration for the song of the same name. Beautiful park and the tours of the home may make you want to go back in time and live there.
http://parks.ky.gov/findparks/recparks/mo/
In the same area is my favorite place in the whole state, Bernheim Forest.
I can't begin to descibe this place, but it is like heaven on earth to me.
Take a frisbee or a ball and glove and pack a picnic lunch. Enjoy.
http://www.bernheim.org/
Wherever you end up spending your time, I hope you enjoy our city and will want to visit again.