I highly recommend Imogene Pass! I've done it in my newer Jeep and my Avalanche. It's a blast!
The trail from Animas Forks up to Stony Pass is a really neat trip with some fun side roads. I haven't done the other side though.
If you're looking for a little more of a challenge in that area, do the leg of Engineer Pass that runs from Animas Forks towards Ouray. Some of the books are calling it by a different name. Something like Mineral Springs.
If you are interested in having the company of someone with wheelin' experience, let me know!
2005 Jeep Rubicon Unlimited - moderately modified
1986 Jeep CJ-7 Laredo - heavily modified
2002 Chevrolet Avalanche - stocker
Now that I've moved to CO from AL, my off-pavement adventures seem to be more about scenery and destination as opposed to what gnarly trail I can conquer. Woo Hoo!