There are not too many in/around Estes. Here is a list of the few I know:
Crosier Mtn. in between Drake and Glen Haven (Singletrack)
Hall Ranch just south of Lyons (Singletrack)
Pole Hill, House Rock, Johnny Park -Estes Park-(Jeep Roads)
There are a couple great rides in Poudre canyon (Hewlett and Young Gulch)
You can also ride UP Fall River Road and then back down Trail Ridge (you cannot ride down Fall River Rd - one way)
Sorry for the generalized info. Let me know if you need more specifics.
there is the devils backbone on 34 from loveland as one goes up the canyon to Estes Park.
there is coyote ridge between 34 in loveland and fort collins off of taft hill rd
there are 4x4 roads north of glenn haven in the storm peaks area
there are trails to seek out in the pingree park area N of RMNP
there is a trail between 34 at mouth of canyon, go north on masonville road by the big thompson school.... between the rock quarries and the little one room mail /post office (cant miss it) a trail there
one can ride Devils backbone N all way up to horsetooth park,