I highly suggest whale watching - Juneau is the easiest place to do it.
In Sitka there is "bears, salmon & Eagles" tour that takes you to refiges for bears, another for eagles, and a hatchery. It is really cool to see wild but rescued aninals that have been saved.
Be sure to count on the shore tours to see Alaska - if you don't take the tours your won;t see the good stuff there.
A helicopter tour to Mendenhall Glacier is expensive but really cool.