SRD v3.5

http://dndsrd.net/
https://srd.dndtools.org/

- Races

https://srd.dndtools.org/srd/races/races.html

- Character Classes

https://srd.dndtools.org/srd/classes/classes.html

- Feat Index

https://srd.dndtools.org/srd/tools/toolsFeatIndex.html

- Variant Classes, Alternative Class Features and Substitution Levels

https://srd.dndtools.org/srd/variant/variantList.html

- Prestige Classes

https://srd.dndtools.org/srd/classes/prestigeClasses.html

- Creature Templates

https://www.realmshelps.net/monsters/templates/index.shtml

- Wizards.com D&D 3.5 archive

https://orbitalflower.github.io/rpg/wizards-3e-archive.html

- Handbook Index

https://minmaxforum.com/index.php?topic=399.0

- WeaselGuy's Index of Handbooks and Guides

https://forums.giantitp.com/showthread.php?654155-WeaselGuy-s-Index-of-Handbooks-and-Guides-(3-x-Ed)