The OSM->Garmin converter, mkgmap, now includes a "marine" style that augments the default style with support for a good number of the seamark tags (lights, buoys, etc.).

This is a work in progress and will mature as the marine tagging matures (polite way of saying, why can't they bloody well agree on what tags to use).

The latest version of mkgmap can be found at http://www.mkgmap.org.uk/snapshots/

Haiti coast with light and wrecks:

Lights/buoys near Kiel: