GSHHS

GSHHS is the "Global Self-consistent, Hierarchical, High-resolution Shoreline Database". It is a high-resolution dataset derived from the CIA World DataBank II and World Vector Shorelines, where all of internal inconsistencies such as erratic points and crossing segments have been removed.

Coverage:
Global.
License:
GPL
Author:
Paul Wessel, Walter H. F. Smith
Download:
http://www.soest.hawaii.edu/pwessel/gshhs/index.html (different formats; shapefile recommended)

Convert to GMT (from shapefile):

ogr2ogr -f GMT output.gmt input.shp