We booked tours for each of our port on this cruise last year. We used a few different companies, but yes, we did book with www.hawaiicruiseexcursions.com
for Hilo, since everyone goes to the volcanoes, we didn't want to do this tour in a big group, which is why we booked independantly. It was a great tour, we were met inside the port by our tour guide, there were only 8 of us in the group and it was $70 for the waterfalls and volanco national park. We stopped at a black sand beach, walked through a lava tube and stopped a a few different gardens. Carnival doesn't offer one tour with all these places, they have it split up into different tours. The tour we booked which was cheaper than the cruise ship tours that were on a motorcoach buses and our tour included more stuff. This was a great tour and was one of the cheapest tours of our vacation. http://www.hawaiicruiseexcursions.com/BigIslandVolcanoIslandTour.htm
for kona we booked with the ship for the Zodiac snorkel trip as the boat are small so we thought there was no concern about being in a bir group with hundreds of people in the water at teh same time. We booked with Carnival for US$115 per person. I later found the same tour on Hawaii Cruise excursions for around $40 less per person. Oh well, live and learn. Didn't do my homework on this one. This was a great tour though, the water is beautiful and it as totally calm when when we were there. I love to snorkel so this was a great way to spend our time in Kona. http://www.carnival.com/Activities/Excursion/191016
For Maui we chose the Rainforest and Waterfalls hike which we booked with Carnival. You do have to be somewhat fit for this tour as the hiking, while not super difficult is a bit strenuous. What was nice was this was a smaller group tour and we got to really see some of the most beautiful parts of Maui. http://www.carnival.com/Activities/Excursion/192012
For Kauai we also booked with Carnival for the Riverboat tour. http://www.carnival.com/Activities/Excursion/193030 We diid like the tour, but wished we had seen more of the island and not just the river and fern grotto. A combination of both would have been better.
For Oahu, we did two tours. One was a Waikiki snorkeling trip that we booked with http://www.hawaiicruiseexcursions.com/WaikikiCatamaranAdventure.htm This was a great day. Nice sail boat and great snorkeling. This trip was really cheap too, for $45.
We also did an island tour of Oahu with http://www.royalhawaiiantour.com/Royal_Hawaiian_Tour/Home.html . This one wasn't worth the money. We were told when we reserved this tour how they have the best guides in oahu but i think they just say that to make you book. Our guide was ok, but by no means was he outstanding. We felt rushed at some of the stops and in the end he made sure we knew that the tip wasn't included. This is a tour I wish we had done with another company.