Another one for Big Thunder. Far more thrilling at night time, in my opinion.
I got the chance to ride Screamin' at about 8:15pm this summer just before WoC and they shut the ride down, and it was superb! Quite different riding it at sunset than during the day.
I also have to agree with the Haunted Mansion and Pirates comments. They do seem to feel more real or something during nighttime.
Never done Splash at night...that's one I'll have to try.