There is a shaved ice shop called Matsumoto on Waialua Bay on Kamehameha Hwy, near intersection of Rt 83 and 99 (near North Shore) that you must try. They have many different flavors and they have a special one where they mix vanilla ice creams, sweet red beans, and shaved ice. My husband tried it and he loved it. I ordered cotton candy shaved ice and it was fun to eat, especially on a hot day.
Next to Matsumoto, there is another shaved ice shop called Aoki, I think, and it's supposed to be good too. If we weren't full with what we had, we would've tried the shaved ice from that shop. Next time we go to Oahu, we will.