Do these types of figures have an official classification/name or are they just "assorted plastic figures"?

Are there any places online I can find a big variety of this kind of thing, preferably less common things like demons, knights, skeletons, etc.

Finally, what are the most unusual ones you've ever found? I found an assortment of ninjas and pirates once, and I grew up on the demon ones you see in the pic, but that's about it.