3D Engines
http://www.cs.tu-berlin.de/~ki/engines.html A big list of 3D Graphic Engines
http://www.47-tek.com 47-Tek sources
http://www.crack.com/golgotha_release Golgotha sources
http://www2.ravensoft.com/source Hexen/Heretic sources
ftp://ftp.3dgamers.com/pub/3daction/00archives/descent/unsupported/d1src.zip Descent sources
ftp://ftp.gamers.org/pub/3daction/00archives/descent/unsupported/d1src.zip Alternate site for Descent sources
http://frag.com/dosdoom The Official DOSDoom Homepage
http://www.genesis3d.com Genesis3D
http://www.xs4all.nl/~frankw WOF engine, a Quake viewer
http://www.planetquake.com/ed3d ED3D, quake editor

3D
http://www.caligari.com TrueSpace homepage, my favorite 3D program.
http://www.3dcafe.com Meshes
http://www.geocities.com/CapeCanaveral/Lab/8572 A Tomb Raider viewer.

Generators
http://www.york.ac.uk/~mpf103/terragen Terragen, Scenery Generator
http://www.diardsoftware.com/universe.htm Universe Generator
http://www.s-direktnet.de/HomePages/tobias_reichert TeraLogic Texture Maker
http://web.singnet.com.sg/~rendsoft Illusionae, Texture Maker

Misc
ftp://wuarchive.wustl.edu/graphics/graphics/books/graphics-gems Graphics Gems
http://www.photodex.com various DOS graphics viewers
http://maps.jpl.nasa.gov Maps of the Solar System
http://www.dictionary.com Dictionaries
http://www.screenshot.com Shareware Download w/ Screenshots
http://www.freeware32.com Freewares
http://www.softseek.com Software Seek
http://www.ocr.com a good OCR program
http://ciips.ee.uwa.edu.au/~hutch MegaHAL (artificial intelligence)
http://www.h-oda.comWCPUID (for cpu identification)