The Open Problems Project - A project to record open problems of interest to researchers in computational geometry and related fields. - http://www.cs.smith.edu/~orourke/TOPP/
Steiner Trees - Open Problems with Steiner Trees, maintained by Joe Ganley. - http://ganley.org/steiner/open.html
Open Problems from the Geometry Junkyard - Compiled by David Eppstein of the University of California at Irvine. - http://www.ics.uci.edu/~eppstein/junkyard/open.html
Open Problems - Collected by Jeff Erickson. Mainly in geometry. - http://compgeom.cs.uiuc.edu/~jeffe/open/