Sublease from other students. Very often students sublease their AYY or HOAS apartments for a relatively long period of time (6 months or more) when they go for exchange, practical training or due to other reasons. Very often subleased apartments are furnished and inexpensive. You can browse students’ ads at these web sites. Some of the ads are in Finnish. You can use Google translate (http://translate.google.com).
Aalto University Sharetribe https://aalto.sharetribe.com
Helsinki University Marketplace https://marketplace.helsinki.fi/en/
Apartments for students in Helsinki Metropolitan Area (Facebook group) http://www.facebook.com/groups/112489548797522/
Forenom provides all sorts of furnished accommodation for short and long term. The rent starts from approximate 500€/month/person. Contact firstname.lastname@example.org or visit http://www.forenom.fi/en/index.html. It is better to browse through apartments yourself in Forenom. If you send an email directly to them it is rarely the case that they answer back with an offer.
Online Notice Boards to rent from private landlords (not students). You can find ads from private landlords through these online notice boards.
Finland Forum. You must register in order to see or place ads. Go to the “Housing” section. http://www.finlandforum.org/
Asuntohelppi. Online notice board with offers from private landlords. http://www.asuntohelppi.fi/ilmoitukset/vuokrataan/index.html
Tori.fi Online notice board with offers from private landlords. http://www.tori.fi/uusimaa/asunnot?ca=18&cg=1010&st=u&w=218&m=313
Vuokra-asunnot Helsinki (Rental apartments in Helsinki) Facebook group (mainly in Finnish) http://www.facebook.com/groups/235368102105/
Uuteen asuntoon vuokralle Facebook group (mainly in Finnish) http://www.facebook.com/groups/35179000735/