To add to Sortaslow's list (also around an hour of Frankfort):
NCT Section A - trailhead is on Beers Road just west of Hodenpyl Dam Road (SSW of Mesick). Big ravines and lots of bench cut trail. Not a loop, so you have to do an out-n-back. I highly recommend this ride
NCT Baxter Bridge/Highbanks Rollaway section - trailhead is on No 29 1/2 road where it crosses the Manistee River (south of Kingsley). A little over an hour from Frankfort. Bring your climbing legs (or bike shoes which are comfortable for walking in
). I have heard this section referred to as the *beep* Bridge section.
Big M - Take M55 east from Manistee to Udell Hills Road. The inner loop stuff is wider (XC ski trails), but the outer loop stuff was designed for bikes. The NCT also passes through Big M.