A lot of course depends on budget. I've heard that the flightseeing tours such as landing on a glacier in a helicopter from Juneau and floatplaning to Misty Fjords in Ketchikan are fantastic trips.........but were really pricey and we didn't do these. For more affordable I suggest a whalewatch trip in Juneau with a side trip to the Mendenhall glacier. Also in clear weather the Mt Roberts tram is wonderful (don't need to pre-book).