The best view of Florence (that I know of, anyway) is from Piazzale Michelangelo, and it's mightly nice at sunset (as you can see). You can see the Arno River, the Ponte Vecchio, and the tower of the Palazzo Vecchio here. If you walk up there, you can arrange to pass by a house that Galileo used to live in. (And don't miss the snow-capped mountains on the horizon; we were there in winter, when there were hardly any tourists compared with the hordes the place gets at some other times of year.)