El Duderino,
Plenty of options, though Winter can be a bit more difficult without 4wd (safety precaution mainly).
As Stan said, peak-to-peak highway always has potential. If you're up for snowshoeing, Indian Peaks Wilderness Area (IPWA) has lots of scenic beauty but will require a couple extra miles of snowshoeing before you get to Brainard Lake and the rest of the IPWA.
RNMP is not too bad right now from what I understand; most of the open roads are reasonably driveable. Bear Lake Trailhead and Glacier Gorge Trailhead 0.5mi before are probably two of the most utilized areas year-round. I'll be heading up to RMNP very early tomorrow morning for a snowshoe trek to Lake Haiyaha and possible Emerald Lake en route back to the Bear Lake Trailhead. If you get into RMNP (passed the entrance station) before 8am, you'll typically not have to pay the normal entry fee. I will say, however, that buying an All Parks Pass ($80/yr) is well worth the money, based on number of National Parks, Monuments, etc that are close to the metro Denver area.
Along the front range, there are a number of hikes out of Boulder's Chautauqua area.
Garden of the Gods in Colorado Springs is always neat.
Heading further into the mountains, you will incur snowy/icy road potential and really have to plan your day-trips, based on road conditions (www.cotrip.org
is a great resource for that!).
PM me if you have more questions. 