Let's kick-start this new conversation space! What's your favorite destination in Finland and why? Let's see if there are any answers other than Helsinki... though I still want to hear from you if that's your favorite. :)
Helsinki is nowhere near as nice as the old capitol city TURKU. Turku was founded in the late 13th century, has a nice big castle near the water and a river running through the heart of town. The city is also heavily swedish-speaking and is the home of Finland's major Swedish-language University Åbo Academy/University of Turku. There's a planetarium, a maritime museum (EXCELLENT http://www.forum-marinum.fi/en/) and on many years the city hosts the tall ships race!
The big ferries (look more like small crise ships than car ferries to an American) leave from Turku to go to Åland and Stockholm through the Åland archipeligo. It's a fabulous trip through a jilloin tiny islands. Taking the ferry from Helsinki is a longer trip that doesn't show anywhere near as much of the archipeligo as from Turku.
Also: the maritime museum in Åland is also excellent. See one of only 2 actual pirate flags in existence. Check out the museum ship Pommern next to the museum. For extra credit take a scuba dive and vist Pommern's sister ship on the bottom of the harbour => http://www.divealand.com/index.php?section=wreckguide&subsection=14
There's a lot to see and do in Helsinki, but I agree that Turku is very nice, with the river, old fort, cathedral, and Luostarinmaki Handicrafts Museum (pioneer village). On the way from Helsinki to Turku by car, we visited Ekenas in the Raseborg area, which is a charming, old fishing village - pleasant to stroll around and have lunch there. We also stopped briefly in Fiskars Village (of scissors fame), now a village for various craftspeople and artists. While staying at Turku, we took a day-trip to Rauma (another old fishing village, this one is a UNESCO World Heritage Site) and the cute harbor town of Naantali.
Poor Finland, I knew this subsection of the Helpline would be almost completely neglected.
I've only visited Helsinki and Porvoo, but here's what I'll say about Helsinki... it's one of those places that I really enjoyed without being able to pin-point exactly why. I've visited grander European capitals, but something about the relatively low-key atmosphere of Helsinki really meshed with me. Put it just behind London and Oslo as my favorite European capital city.