In 1996, D.E. Joyce (Clark University) constructed an interesting web site that should be of interest to anyone who enjoys teaching geometry, studying geometry, or exploring the history of mathematics.
Basically, the site is an interactive "reprint" of Euclid's Elements (Books I-XI). With each proposition, the user can manipulate the diagrams (i.e. constructions) to better understand what the proposition is claiming (and its associated proof).
The commentary is a great help, though not on the order of Heath's translations. If you have never actually sat down and read Euclid's wonderous text, do so...and be prepared for some surprises of "breathless length."
Source: Euclid's Elements link