If you want a fun moderate trail with your rig, do the Middle St Vrain/Coney Flats trail. It's about a 3-4 hour trail and you'll be fine with 35s and 3.73s. If you have 32s stock, you'll be fine and no need for the disconnects. I have 3.73s and 32s and did it, there's some light to moderate rock sections with great views and a good chance of seeing moose. Youtube has lots of videos on this trail as well. The earlier you get up there, the better as there will be less traffic on the trail, some of the spots are not cool if you have oncoming traffic (too narrow). Make sure and air down on that one too, some mud and lots of rocks.
Also as a previous poster suggested that book, definitely get that book, great resource.
I've also included a USFS Land use map :
http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5165768.pdf
If you zoom in on it, there are black/white checkered lines (use the key and you'll see). These are all forest roads and 4x4 roads. I would suggest researching each road via google too to make sure you don't get in over your head. Miller Rock is a trail that has some good rock crawling from what I've heard too.
So I ended up moving to Brighton, Colorado. I'm here and itching to go on a trail. What trails aren't too far away that I could run. I currently have my stock sport tires on but could put my 35" m/t back on ( except I'm running 3.73 still with 6spd ). Would I have to disconnect my swaybar links for the trails? Either way my wife and I really want to do a trail in the mountains. I told her you guys were the ones to ask lol
