BikeKatyTrail.com is a site with all manner of information about the Katy Trail, destinations, accommodations, and travel information. It has an active discussion area. Highly recommended!
The 2004 MS150 used a nice route (see map, PDF format, 6 MB) from the Kansas City area to Windsor, which is near the western end of the Katy Trail. Combining that map with the second day map (PDF, 4MB) also gives a nice route from Sedalia to the Kansas City metro area. For ideas about getting from anywhere in the KC Metro area to the starting point of these maps, look at this bicycling map of Jackson County, MO.
The American Discovery Trail--a network of on- and off-road routes stretching from the Atlantic to the Pacific oceans. The route through Missouri goes from St. Louis to Kansas City and uses the Katy Trail to cover much of the distance.
Northland Trails & Greenways and Northland Trails Vision Plan--planned multi-use trails throughout Clay and Platte counties. Right now most of these are still in the planning stage; a few are under constructions and a few more are already on the ground.