I own 3 D20 System monster books: Fantasy Bestiary, Creature Collection, and Primeval Groves. I've used one monster from Creature Collection, and everything else comes from Fantasy Bestiary. Except for mundane animals--that's the only thing i've used from the D20SRD, and even then, more than half of them i had to invent myself (the only herbivores are elephant, donkey, & horse) and the rest all had to be tweaked to have some semblance of realism.
Even if i didn't have access to the D20SRD, nothing in the MM would be worth buying it.
Even if i didn't have access to the D20SRD, nothing in the MM would be worth buying it.