Rock Cut overlook (off Trail Ridge Rd.) looking to Longs Peak at sunset. You can end up with something like this:Sunset at Rock Cut
(This was back in my early days of photography, so I didn't know about all the tricks like blended exposures, etc - all I'd done was hit it with Auto Levels).
Alternately, if you're a morning person, hike up Twin Sisters (3.5 mi one-way) and get the east face of Longs Peak at sunrise.