Do a helicopter tour of Kauai, especially the Napali coast. It's stunningly beautiful and can really be appreciated from the air. Waimea Canyon is beautiful from the air too. Helicopter tours are amazing; they play music while you take in the sights. We did one in 2001 and it was worth every cent. Kauai is under-appreciated.
On the Big Island, drive out to South Point. It was very isolated and stark but beautiful. Enjoy!