Might as well start a thread for Ohio -- I try to only post places I've actually been to and have experience with.
http://crowcanyonmx.com/ -- 400 acres of some really good woods riding available, along with an MX track, I've been here several times and really enjoy the trails... they have some really tough/technical sections and some really easy stuff - and everything in between.
http://www.beansbikepark.com/ -- 100 acres with trails and an MX track. I've not been here yet, but I should hit this place sometime in the next month - will update after I go. Normally I wouldn't have put this on the list without going, but I was told the place is nice from more than one person.
http://www.krashracingdirtpark.com/ -- I've only been here for a harescramble race, but they are open for play riding... the trails were very good and technical during the race I was at. I will try to get out here again for just trails and post an update.
http://humboldthills.com/happyhollow.html -- I've only been here for a harescramble race as well. Plenty of good sections in the woods - nice hills and some big rocks here and there. The site says they have open practice - maybe someday I'll hit it as well for just play riding.