I don't what material is OGL content from the following, but these are third party d20/OGL products that I would look at:
Fantasy Occupations (Adamant Entertainment)
Cavalier's Handbook (Green Ronin) except for the class itself
Psychic's Handbook (Green Ronin)
Shaman's Handbook (Green Ronin)
Witch's Handbook (Green Ronin)
Holy Warrior's Handbook (Green Ronin)
Unholy Warrior's Handbook (Green Ronin)
Hong's Knight (Hong)
True20/Mutants and Masterminds (Green Ronin): True20 Conviction/M&M Hero Points and rules for what they can do, Pushing Rules, M&M Complications, True20 Classes, True20/M&M damage system
Book of Iron Might (Malhavoc): Maneuver System and Fighter Fighting Styles
Scrollworks issue #? (Scrollwork Press/Christian Walker): Fatigue and Exhaustion from Hit Point Loss by Michael Hammes
Poisoncraft (Blue Devil Games): Poison rules
Artificer's Handbook (Mystic Eye Games): Slot System Magic Item Creation
Advanced Rules for Beginners (EN Publishing)
From Stone to Steel (Monkey God/Highmoom Media)
Airships (Bastion Press/ Dragonwing)
Bestiary: Predators (Betabunny)
Sharks! (Bards and Sages)
Snakes! (Bards and Sages)
Spiders! (Bards and Sages)
Advanced Bestiary (Green Ronin)
Book of Templates (Silverthorne/Goodman Games)
Book of Fiends (Green Ronin)
Noble Steeds (Avalanche Press)
Experts 3.5 (Skirmisher Press): even without the expert classes, but the rest of the material is great for DMs wanting to world building.
Beyond Countless Doorways (Malhavoc)
Tournaments, Taverns and Fairs (EN Publishing)
Alchemy and Herbalists (Bastion Press/ Dragonwing)
Torn Asunder (Bastion Press/ Dragonwing)