I've been using a high density external floppy for a long time on my Amigas. It's called the XL Drive made by Power Computing Ltd.
It supports Amiga disks (1.76MB) and IBM formatted disk (1.44MB), think it even supports Atari floppies but I've never tried it myself. Requires WB2.1min. A driver is required to be setup in S-S to have the HD capacity else drive just works as normal Amiga FD.
