K&K's Mandolin Twin Internal is a personal favourite. I've fitted it to everything from a cheap oval-hole to a Collings MF-5 and it always delivers. Fitting the endpin jack is slightly trickier than a guitar as you usually have to drill through the tailpiece as well as the endblock. For information about fitting, see this project page.
If you don't want to modify the tailpiece, the Mandolin Twin Fusion is a good alternative, as it uses an external carpenter jack mount for the jack socket.
The Banjo Twin works well on pretty well any banjo, from old-time to bluegrass or tenor. It uses a semi-floating design, attached to the underside of the head and the perchpole or compensator rods.