Just got back from 5 days in Waikiki and 5 days in Maui.
hawaii23.com worked awesome. A guy named Alex (Mark subs out to some taxis), was 5 minutes early picking us up from the airport. He drove a clean, newer Toyota Sienna. $23+tip is a steal to get to Waikiki. We were so impressed, we got our friends to use him on their way back to the airport. He was right on time for our trip back also.
Best shaved ice in Waikiki is in the weirdest of places. It's downstairs in the Waikiki Shopping Plaza, right when you go down the escalator from Kalakaua. It's a shave ice/sandwich shop called Ailana's. A family run shop but usually you'll find the son working - nice, friendly guy and he'll let you try different flavours. It's light, not compacted and a lot of the syrup is made w/ real fruit. Our fav was strawberry and haupia (coconut) w/ sweetened condensed milk ice cap.
Ailana Shave Ice Waikiki - Waikiki - Honolulu, HI
Awesome udon at Murukame Udon, just a block from Kalakaua, on Kuhio. Cut through Dukes Ln, beside the Holiday Inn and you're right there. There's usually a line outside but it moves quickly.
Marukame Udon - Waikiki - Honolulu, HI
Shrimp trucks on the North Shore. They're all pretty good. We liked Fumi's but you can't really go wrong w/ Giovanni's or Romy's either. While you're at Giovanni's (the big one), check out the BBQ'd corn stand, Filipino BBQ skewers and a bit off to the side but in the same lot, the orange Thai food truck had pretty good, authentic, pad thai.
If you're interested in tandem skydiving, I had a great experience at Skydive Hawaii on the North Shore. With online discounts, it was only $150. Of course, video and pics are available but they're fairly costly. I suggest going with a friend cause you might have to wait a while for other groups to go up. Shuttle service was free from Waikiki hotels. I got lucky and went up with a Russian skydiving team and ended up jumping at close to 19,000ft.
Skydive Hawaii - Hawaii's most exciting activity tandem skydiving in Honolulu Oahu Waikiki