This is a fantastic question. The entire resort transforms itself at night and assumes this entirely unique energy. Even the lands and attractions that you’re familiar with become a new experience. The rides that I would recommend riding at night are rides that are outdoors or have an outdoor segment.

Disneyland Park:
-Main Street, U.S.A.: just take some time wandering along the street, sipping some hot chocolate and nibbling on a cookie from the Market House while admiring the popcorn lights that illuminate the land.
-The Jungle Cruise: for an extended period of time, I only rode this attraction at night because I love the nighttime experience of this ride. The darkness of the jungle is both mysterious and enchanted, and when the animals are half-draped in shadows, they become even more realistic and believable.
-Splash Mountain: I can understand why anyone would be hesitant to ride this attraction at night, but sitting towards the back rather than the front will drastically reduce your risk of getting wet, minus a few drops. After the first drop, as you come around the bend, the view of the park in the moonlight is amazing.
-Big Thunder Mountain Railroad: the way that mountain is illuminated at night is spectacular. Along with Splash Mountain, it’s fantastic during the fireworks. It’s amazing to come out of a tunnel and see the sky illuminated in their colorful fire.
-Storybook Canal Boats and Casey Jr. Circus Train: both are charming rides during the day, but have a different type of magic at night that’s truly worth experiencing. The way that the miniatures are light up make them pop against the darkness of the water and the vegetation.
-Autotopia: it’s different zipping around in those little cars when the track is lit up by lights rather than sunshine.
-The Matterhorn: the darkness adds to the mystery and excitement of the ride.
-Various outside restaurants: dining locations that feature outside seating, like the courtyard in Rancho del Zocalo, are fantastic at nighttime.

Disney California Adventure:
-Cars Land: the way that the entire land becomes illuminated by the glow of these colorful neon lights is magical beyond words and extremely effective at embracing you in this alternate place and time. If possible, I would recommend trying to be in the land as the sun sets, when the lights are turned on.
-Radiator Springs Racers: the way that Cadillac Range shines in the darkness is breathtaking, and even during the racing segment, conveys peaceful feel.
-Mad T Party: it’s interesting to see how Hollywoodland becomes completely transformed once the sun goes into a crazy dance party.
-Grizzly River Rapids: this attraction I have never rode at night, because unlike Splash Mountain, you are practically guaranteed to get wet, if not completely soaked. However, I can only imagine how gorgeous this attraction is at night as you float through the rivers of the mountains surrounded by ancient rocks and beautiful redwoods.
-Grizzly Peak: spend some time in the land of Grizzly Peak, admiring the silhouette of .the mountains and the towering redwoods. The land does an exceptional job at capturing the magic of the mountains at night.
-Paradise Pier: this is another land that assumes an entirely new personality at night with all of the popcorn lights and kinetic energy of the land. Just remember, that the attractions of the land will close with the first showing of World of Color, so ride them early in the night!
-Mickey’s Fun Wheel: an extensive and beautiful view of city lights slowly comes into view as the ferris wheel turns and you advance higher and higher into the sky.
-California Screamin’: it’s incredible how the coaster’s tunnels and the popcorn lights of the track glow in the darkness. And that view of the city as you climb the attraction’s main lift hill? Words cannot describe this experience. Another prime time to experience this ride, along with many other outdoor rides, is during sunset. A pink/red/orange sky as far as your eyes can see is truly a sight to behold.
-Tower of Terror: although the majority of the ride takes place indoors, when the doors open during the drop sequence to reveal how high you are, you’re treated to an incredible view of city lights. Once my friend rode Tower of Terror during the fireworks show and enjoyed of a sky filled with fireworks.
-Buena Vista Street: the Carthay Circle Theater is breathtaking and its creamish-white structure seems to glow like the moon in the sky. Order a latte from the Fiddler, Fifer & Practical Café and enjoy it by the fountain.

Downtown Disney:
-Get some Häagen-Dazs ice cream and consume it while enjoying the music from some street performers. My personal favorite is the violinist. If you see him, request "Con te partirò" ("Time to Say Goodbye") & enjoy the beautiful music.

The absolute best thing to do is to go on splash mountain at night during the fireworks. You really don't get that wet at all and you'll have a perfect view of the fireworks on the ride. Also, the line will be short because not many people go on at night AND people are watching the fireworks. Hope this helps.
P.S. it's always best to do things when shows or parades are going on because people will be watching that.