Two charity organizations, UFF (non-religious) and FIDA (christian) collect used things to raise money. You can check where to take your stuff from their internetsites:

UFF http://www.uff.fi/vaatekerays/kierratyspisteet.html

FIDA http://www.fida.info/fi/fida-lahetystorit/kierrata-lahjoita-tavaraa/kera...

Also a good place to take reusable things is the Helsinki metropolitan area reuse center: http://www.kierratyskeskus.fi/in-english. Thay can even pick up used furniture etc. from your home.