As you mention Estes, the Pole Hill trail, close to Estes, is a decent, shortish trail. Make a stop at an overlook or two.
I asked a similar question on a local 4x4 forum for "which scenic trail" and this is a list that came up:
Wheeler Lake, Brody, Classic trail, can be bumpy & slow
Twin Cone, supposedly graded, stellar views
Bill Moore Lake
Mill Creek Loop
Grizzly Lake, pretty tame after the first challenging obstacle, pretty area
St John's Mine
St Mary's Glacier
I promote and like the FunTrek's books (have NoCo, SoCo, Moab) though www.TrailDamage.com
is another good resource available.
You can list trails by many categories (scenic, difficulty, etc) and they have a google maps function showing trail locations respective to the state.
To start a scenery sort (select Colorado for the state). Most scenic looks to be at the bottom of the list (least scenic at the top).
Trail T-33a, south of Estes Park a bit might be of interest if you're into airplane wreckage.
Some info from my 2012 visit: