My wife and I are planning a trip to Hawaii at the end of May, we have tickets booked in and out of Maui. Any suggestions on must do activities?

I have been to Maui before and am already planning on Hanna Highway and Mt. Haleakala. Is there any good SCUBA diving? Would it be worth taking a couple of days to go to the Big Island?

Oh, and great restaurant recommendations would be appreciated too!