J-D. Boissonnat et al.'s code for Delaunay meshing in 2 and 3 dimensions in C++.
http://www-sop.inria.fr/prisme/logiciel/del-tree.html
By Martin Held. Copes with polygons with holes and degeneracies/self-intersections; based on repeatedly clipping ears. Source code on request.
http://www.cosy.sbg.ac.at/~held/projects/triang/triang.html
Arbitrary length FFT C-source, 3D gravity simulator, quantization of FIR filter coefficients. C source.
http://home.get2net.dk/jjn
http://www.complextoreal.com/tutorial.htm
Source Code in Fortran for FFT from "Programs for Digital Signal Processing", 1979, IEEE Press, ISBN 0-87942-127-4. The book is necessary to use and understand these source code listings.
http://members.tripod.com/michaelgellis/dsp/pgm05.html
Links and various Fortran FFT implementations.
http://ourworld.compuserve.com/homepages/steve_kifowit/fft.htm
http://astronomy.swin.edu.au/~pbourke/analysis/dft/
FastGEO, A computational geometry library written in the object pascal language.
http://www.partow.net/projects/fastgeo/index.html