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Allevents.in has a nice list of parties in Helsinki.
PictureTavastia Club
The Tavastia Club (Finnish: Tavastia-klubi) is a popular rock music club in Helsinki, Finland. Tavastia is located in central Helsinki Kamppi district on the street Urho Kekkosen katu. It has a capacity of 700 people.
PictureOn the Rocks
Located in the absolute center of Helsinki, On the Rocks is a live music rock club and street bar for everyone looking for a cool place to hang out, relax and listen to good music or check out some great live bands. On the Rocks is right next to the Central Railway Station, at Mikonkatu 15. They have live music, stand up, jam nights and great dj’s – and they are open until 4 AM every night!
PictureApollo
Apollo live club. The former movie theater setting gives this club a special atmosphere. We have really enjoyed the live bands playing there when we have visited the place! 

Arrive early to reserve good seats in one of the boxes above the dance floor and before the band starts to play, spend the time by watching music videos projected on the big screen...
PictureNosturi
Nosturi is a versatile live music venue located close to downtown Helsinki, operated by the Live Music Association (ELMU ry). Nosturi takes pride in providing a platform for a broad spectrum of culturally relevant events such as concerts, raves, youth discos, theater and art gallery functions from all walks of life - everything from unknown underground bands to the largest mainstream acts. Also provided are rehearsal spaces for 40 bands.
PictureCircus
Circus. A modern venue for concerts with a capacity of 1500 people right at the city center.
PictureStoryville
Storyville. If you are looking for live Jazz music and a place that is open till the wee hours in Helsinki.. Storyville is the place! Most nights they have a jazz bands playing and the place is quite lively...a dance floor for those willing to shake a leg...
PictureHall of Culture
The Helsinki Hall of Culture is a multi-use venue for culture, events, and conferences. The Helsinki Hall of Culture was designed in the 1950s by Alvar Aalto, and the magnificent building exudes the atmosphere of years gone by, providing a fantastic setting for a wide range of events.
PictureHelsinki Music Center
The Helsinki Music Centre, located in the heart of Helsinki, is a concert venue and meeting place open to all.

In addition to the 1,704-seat Concert Hall, intended for acoustic music, there are also five smaller halls in the Music Centre—Black Box, Camerata, Organo, Sonore, and a Rehearsal Room—and the Klubi Restaurant, all of which have different acoustics and uses.
PictureHartwall Arena
Hartwall Arena, often called Helsinki Areena, is a large multifunctional indoor arena located in Helsinki, Finland. The arena gets its name from its largest sponsor, the beverage company Hartwall. The arena is situated next to the Pasila railway station, which is the second busiest railway station in Finland, 3.5 km north of Helsinki Central.

Total capacity in ice hockey games is 13,506 (all seats). The arena is convertible for various events. For sport events, the capacity is about 10,000, about 14,000 for basketball, for concerts about 13,000.
PictureSavoy Theatre
Over the years the Savoy Theatre has provided an important and colourful addition to Helsinki’s diverse cultural life. The Savoy Theatre is especially well known as a concert venue for world music. Each year around 200 groups from around the world perform at the Savoy Theatre. 

The Savoy Theatre is situated in the center of Helsinki just off the Esplanade Park.