Natural Pumice Stone
There are pumice stones and pumices stones, these are definately the latter, they're as black as Voldemort's heart, they're straight out of the volcano that formed them and they're quite, quite beautiful. We all know pumice stones are useful things to have around if you have feet, but it's also nice that they're attractive. No reason functional things can't also be beautiful, is there?
The colour of these makes them particularly suitable for modern stylish bathrooms, but also, because apparently it's an actual law that men's things must be black they make great gifts for guys.