At night the city has more to offer than probably all other american cities together (Las Vegas excluded). And as long as you stay one the main roads there is nothing to fear. I know places in Stuttgart, Germany - I live there - where I feel substantially more uneasy after sunset than in New York.
1.-3. View
Taken on Empire State Builing in 1994
4. Times Square
Lightshow around Times Square and Broadway
5.-9. Nightimpressions
Images from Midtown