Geometrical figures

Just a little note for myself here, but Geogebra is probably one of the best ways to manipulate geometrical things right now. We did some diagrams in InkScape for a LaTeX paper, but it really wasn't ideal.

That said, though, PGF and TikZ seem to be the best-practice approach in the LaTeX field (not a graphics editor, but a description language).

GEOS

An open-source geometry library.

Graphical generation

Just a note for my later amusement: I've been thinking of the automatic generation of graphical forms - specifically, 19th-century masonry.  I want a city generator that does for me what London or Richmond, Indiana give me - shivers down my spine that I don't even understand.