Chemtool is a GTK+ based 2D chemical structure editor for X11. It supports many bond styles, most forms of text needed for chemical typesetting and splines/arcs/curved arrows.
Drawings can be exported to MOL and PDB format, SVG or XFig format for further annotation, as a PiCTeX drawing, as a bitmap or as Postscript files (several of these through XFig's companion program transfig).