Hippocampus aren't helpful, just non-threatening
Centaur are often portrayed as friends of humanity - Chiron in particular.
Satyr follow the same vein as Centaur
Merpeople in moden adaptation are usually friendly, the original ones were not however. You're right, they'd lure people to there deaths. Where they differ from Sirens is in the fact that sirens sing to sailors in order to lure them, also they are not part fish in appearance but are instead part bird.
Lycan are sometimes made out to be nice, providing they can control the curse, as are Vampires.
Most mythical animals as opposed to creatures... Pegasus, Phoenix, Unicorns etc are usually put across as being nice.
That's greek myth. I can go on if you'd like?