What services which allow to multiply our STEEM (Steem Power/ by leasing etc) are the most attractive now?
What are the ways to earn additional STEEM at all? I heard about services which allow to delegate votes or so - I am looking for the best way to allow my SPs to not lay useless when I am not using steem

Delegate to a bid bot such as smartsteem or upmewhale and they will send your share of the bids daily.
That may not be the highest return possible (and probably isn't) but it is definitely the easiest by far.
You can find a list of operating bid bots here:
https://steembottracker.com/Isn't there a more ethical way to earn rewards on our stake?
Not that I'm completely against bid bots, but I'd rather invest in something that benefits Steem overall.
Also, surprised to see you here, didn't know you were an active Bitcointalk user