Here are some of the resources I use:
- Dingle's Games - 3.5 Monster and NPC generator. Free but more features with paid membership.
- Random Wizard Spellbook - 3.5 Spellbook generator. List random base spells and has random spell generator for each level.
- Seventh Sanctum - Generators - NPC flavor generators for multiple systems and genres. Generate names, history, personality, descriptions and a bunch of other random stuff.
- IMarvin's Token DB - 3.5 Monsters. This is a must have for MapTools.
- Donjon RPG Tools - Another Random Generator site. I used it for magical items but there are some other interesting tools there like Power Attack calculator.
- 3.5 XP Calc - I like this one because it's not limited by level 20. It also includes advice, treasure value and other stats about encounter.
- Javascript D&D 3.5 Character Generator - This is a fairly good Character Generator with many options.
- PCGen - Application that downloads to your system to create PC, NPC and Monsters for various systems.