There are numerous places to get the skyline of LA, esp. if you're interested in including the downtown buildings, the two most classic being from Griffith Observatory (which is also great for night architecture photos) and Kenneth Hahn Park, but KH closes at Sunset.
One thing to be careful with, though, at the Observatory: crowds. I tried to get to it last night to show it and the view to my parents-in-law, about 1930 hours or so, and the line of cars from both direction was astounding. Never seen the like of it before there, AND there was a concert going on at the Greek Theater, just down the hill. From the Fern Dell direction, for some inexplicable reason, they weren't even letting cars into the upper parking lot.
There are also numerous pulls-offs from Mulholland Drive, the best probably being the Hollywood Bowl "Overlook".