Chang e the mood
Instead of keeping the light even across the shot with fill-flash, try taking a darker, more moody-looking shot. A narrower aperture and lower ISO will darken the scene. Expose for the sky, so that the foreground is more or less completely dark, then fire your flash on a higher power to use it as the primary light source. This will give a high-contrast effect, almost as if shooting at night, while keeping some detail in the sky for a balanced image (see page 42 for more on this technique).