Here's the spots we've used in the past:
1. Sunrise Mountain, which is BLM land with several public parking
areas that look down upon the city. Take Lake Mead Blvd. east from I-
15 in North Las Vegas several miles until it winds up onto the
flanks of the mountain. Get there early as this is always a
popular "city lights" viewing spot.
2. Horizon Ridge Parkway, in the south vallley connecting southwest
LV and Green Valley. There are several good vantage points of the
city from here; you might have to park in some professional
building's parking lot, but no one will really care.
These first two spots are somewhat distant, but give a good overview
of the valley. The next two spots are closer:
3. The airport viewing area along Sunset Road will also give you a
good view of the Strip fireworks. Get there early as there's only
room for about a dozen cars.
4. The neighborhood area just above Decatur between Flamingo and
Spring Mountain has a tremendous vantage of the Strip (it's located
on the side of a hill). Go there and find a useful parking spot.