The insane hairball that is the world's timezones has been rendered as a free/open shapefile for all your cartographic/temporal needs. The project, maintained by Eric Muller, has been going since 2008, and is a work of data-heroism, given how totally screwed up and complex the world's timezone divisions are.
The tz_world shapefile captures the boundaries of the TZ timezones across the world, as of TZ 2011b. The geometries are all POLYGONs, and a TZ timezone will sometimes have multiple polygons. There are about 28,000 rows.tz_world, an efele.net/tz map (via O'Reilly Radar)
The tz_world_mp shapefile captures the same boundaries. The geometries are either POLYGONs or MULTIPOLYGONs, and there is a single geometry for each TZ timezone. There are 394 rows.
There is a companion map for the TZ timezones used in Antarctica stations.
The geometries are primarily derived from the fip10s data (itself derived from the VMAP0 data), augmented with data presented in the pages for the maps of the United States, Canada, Russia and China.