At the NE corner of the fountains, you can use the 3rd pillar from the Bellagio shops to get a nice, unobstructed shot of the water show, with the Cosmopolitan and O sign in the background.
Go inside and up to the top level. Pick an end of the building, depending on the light, and shoot straight across at the clock. The lines of the glass on the ceiling create a very interesting effect.
