I'm starting to put together some DIY itineraries for Copenhagen, Stockholm, and Helsinki (haven't gotten to Tallinn yet) and was wondering just how many others we were going to run into on our days!

What things are people planning for these ports? Here's what I have tenatively scheduled out:
Copenhagen Day 1: DIY North Zealand castles tour (Train to Fredriksborg Castle, Train to Kronborg Castle, Train back to port area) - might try to hit Tivoli in the evening to see it with the lights on.
Copenhagen Day 2: Canal boat tour, Tivoli, Stroget
Stockolm: Bus to Vasa, Walk to Skansen, bus to Gamla Stan, Rick Steve's Gamla Stan walk
Helsinki: ?? Still working on it. I kind of want to see the Rock Church, and DH is interested in Suomenlinna. I'm tempted to take it easy and just wander the Market Square and areas since we'll have so much touring behind and ahead of us!
We're planning on getting the Copenhagen Card and the Stockholm Card - both include public transit and entrance to the places we're looking at going. The Helsinki card is tempting, but we might not use it enough to make it worthwhile.