Some people now prefer more exotic places to visit, but for me, Hawaii stands alone in terms of the diversity it offers.  I've only been to Oahu (many times) and Kauai, but I've seen all I need to deem it one of my favorite places in the world.  Oahu has a little bit of everything.  You've got some city life in Honolulu, then outside of that there is lot's of lush countryside and tons of good waves if you like to surf.    Kauai is much quieter and doesn't really have a city, just a bunch of little towns, but it's absolutely gorgeous.  The north shore has one of the highest annual rainfalls in the world and is just stunning.  My wife and I stayed on the other side of the island in Poipu and when we went to the north side we found this unbelievable beach that we had entirely to ourselves.  It was like a dream.  I could go on and on, but I suggest you check it out for yourself.  I'm going to Maui this summer and then back to Oahu before heading back to the mainland and I can't wait.