The only weekly social at the moment is AfroLatin Night at Uggla nightclub on Mondays.
For what it's worth, here's a list of salsa dancing possibilities (parties, events, dance schools, etc) in Helsinki that I collected:
[
Salsa in Helsinki — a guide for social dancers]
Edit: Well, Salsa Forums prevents me from posting that because I haven't been chatting on this forum enough. Whatever.

You can re-create the link manually by removing spaces:
www . evernote . com /shard/s59/sh/d7452f1f-758c-495b-a861-068c6936f7c5/9d56c7313a0b9c908de202866e36a590
I'm trying to keep that reasonably up-to-date and comprehensive (though admittedly I don't know the CBS scene so well).
I agree that Uggla on Mondays (AfroLatin Night) is the best* weekly bet. It's a really nice, friendly social dance; whether you dance CBS, Cuban, kizomba or zouk, you'll get your fix. The playlist is a little thin on bachata though, in my opinion. (* Except during summer when Oopperasalsat is on. That party is totally awesome.)
"La Mega Rumba" mentioned in the previous message never got off the ground unfortunately (cancelled after 3 or 4 weeks). But there's quite a lot of stuff going on, with many occasional or semi-regular parties, totalling around 2–4 salsa or latin parties every week.
Especially Baila Baila dance school has been notably active in organizing rather big parties on a semi-regular basis (usually Saturdays). Strong Cuban style dominance, but the music is not all timba, and it can be fun for any dancers. Events section on their website shows what's coming up: [google up Baila Baila -> Events]