Comments made to our Dark Souls Wiki
By Anonymous
I haven't seen this in the comments here yet, so I'll add it.

The Pisacas in the Duke's Archive (the blue, tentacle headed serpents outside of Big Hat Logan's cell) also seem to have a decent Humanity drop rate. Don't have data on the rate, but even with only 1 humanity, not augmented by equipment, I would get one every run or two.

The main drawback to this method is the long distance between the bonfire and the Pisacas. It can be a lengthy trip, although not a dangerous one. In fact, there are no hostile enemies, so long as the music on the player is turned off.

Can't recommend enough, especially if you're a ranged fighter grinding for both humanities and souls. The Pisacas won't become hostile unless attacked or you get too close (again, so long as the music is turned off).
By Anonymous
Damn you’d think after being dissected for over 10 years in every which way there would be more concrete information on this. I know the rare stuff really just comes down to RNG but youd think we’d have official drop tables and such by now.