Because our family has a B&M collectibles business, my parcels are insured by Hugh Wood International, a specialist insurer, based in Britain whcih has offices in Toronto.
They cover our store, including fire , water and shoptheft, travel to shows, shipments, consigned items ... and all for less than most of the big insurance companies, because they specialize in insuring collectibles, both for dealers and collectors.
For one-off or occasional sellers, I have heard nice things about shipsurance.com.
Many postal services automatically carry insurance, but not all of them.
Many courier services automatically carriy insurance, but not all of them
And then there is Cookie Jar Insurance, for low value items.