I've seen/heard of yarns spun from alpaca, bamboo, posum fur, musk ox and camel hair as people here are mentioning, bunny fur (angora) hemp, milk, wood pulp, rayon, sea kelp, linnen, and coffee filters to name a few other options.
I personally like alpacca best for the softness, although I've never bought any really pricy luxury fibers like cashmere or qivuit.
Acrylic can vary a lot in quality. I'm knitting my first sweater in acryclic yarn because it was a gift and I figure my first sweater will have tons of mistakes so why spend a fortune on it--but the yarn actually squeaks sometimes it's soo plasticy. But I have seen some acryclic which is soft--I think it's better in wool/acrylic or alpaca/acrylic blends, which I have knit with.
But dang, if I'm not curious about that possum fur.