I am allowed to use the SRD books in a 3.5 campaign. Which books are SRD and what books are not in D&D 3.5e?
The d20srd FAQ appears to answer this for us, rather helpfully, in a question about future content:
This site currently contains content from all sourcebooks published by Wizards of the Coast that contain open content. This includes open content from the following books published in the official d20 SRD:
- Player's Handbook
- Dungeon Master's Guide
- Monster Manual
- Epic Level Handbook
- Deities and Demigods
- Expanded Psionics Handbook
In addition, the following open game content has also been included:
- Razor Boar and Scorpionfolk from Monster Manual II
- "Variant Rules" from Unearthed Arcana
However, not all content of these books are covered in the SRD, and sites like D20SRD are not permitted to publish it. For example, some monsters are considered product identity and omitted.