My very favorite excursions have all been in Alaska. Whale watching - every time I go, it's a beautiful, spiritual experience. I'm glad that I've taken the smaller "speed" type boats during these excursions because we get from location to location quickly as the captain stays in contact via radio with (I'm assuming) spotters. NEVER been disappointed and would go back in a heartbeat!
Also in Juneau, the Taku Lodge floatplane trip is well worth the money. A beautiful flight up over the mountains & glaciers. Each passenger has their own window, headset for narrative. The views are indescribable! Lunch at the lodge was wonderful and the surroundings were amazing. I had a horrid fear of flying up until the year I took this excursion & it cured me! A man in our group was allowed to sit in the co-pilot seat on the flight out, so I asked the pilot if I could sit in the co-pilot seat on the flight back and he let me!! My husband could NOT believe I was actually doing this but I was determined to conquer my fear. Now, I LOVE to fly.
I also love the White Pass Railway trip out of Skagway. I'm a train nut so this is a "must-do" for me when I'm in AK.