"You don't want to get a toad, they're out of fashion."
-Rubeus Hagrid (PS5)
Toads are allowed as pets for students at Hogwarts, but they’re out of fashion, so if you have one, you’re likely to be laughed at for it. Nevertheless, Neville has a toad named Trevor, a gift from an older family member (PS6, Pm), and there are enormous purple toads in the Magical Menagerie (PA4).
Judging from Mundungus' story on Harry's first night in Grimmauld Place, toads (at least in bulk) are valuable enough to go to quite a bit of trouble to steal (OP5).
Toads have been associated with witches since the Middle Ages, when they were believed to be familiars and possess magic.