Any sort of budget in mind?
Flightseeing tour should be memorable and cover a lot of ground (fly out of Willow/Talkeetna/Wasilla). Can do glacier landings, Denali, etc. Probably run you around $300/person.
Drive out past Chickaloon and go see the Matanuska Glacier up close and personal. Depending on conditions/activity level of folks, climb Lion Head and get super views of the glacier and adjacent mountains (take some good binoculars/spotting scope and see the sheep on the mountains to the north).
Hatcher Pass is always good. Depending when exactly you go, the mine still may not be open (nor the road up to it, but you can still hike to it...just may be some snow still). Several trail systems within the area itself, things may be a bit muddy though with everything melting
same with the Lion Head suggestion above, or any other outdoor activity really.