Eurohostel is the classic budget place to stay in Helsinki. Frankly speaking I'm a bit disappointed with it now, but it still has its pros:
-Moderate prices
-Relatively good quality of service
-You pay only for the things you need
-Great view of the Helsinki bay and ferry terminals from the window (it will remain until next year - they're building a house in front of the hotel)
-Great location (it's on the Katanajokka island - just a 5-minute walk from the Kauppattori)
-An idyllic surronding: ferry terminals, old brick houses and small parks
-The morning sauna is included in the price.
Drawbacks:
-Well, it's a real hostel. The bathrooms and the kitchen are in the corridor.
-Rooms have a "worn"-look. No renovation since 1998.
-The breakfast is to be paid separately and is too expensive. You get just a small choice of food and not a Swedish table, as stated.