You could always check out the two mosnter supplements over at The Burnt World of Athas, Terrors of the Deadlands (25 unique undead, 19 undead templates, and 18 verminous beasties) or Terrors of Athas (200+ monsters and seven templates). All free for download. Its all campaign specific for Dark Sun, but its all 3.5 compliant so it ports over into any setting with only minor tweaks of flavor text.
www.rpgnow.com has a whole section on d20 creature pdfs for sale. Minions Complete, Legacy of dragons, GF Monsters, Book of Templates, Book of Templates Deluxe, Bane Ledger, and Terrors of the Twisted Earth are all pdf creature books I have that I would recommend.
For free ones there is www.opengamingfoundation.org to link to the 3.5 srd. And from there you can link to the d20 modern srd which has some more monsters.
In my sig there is a free preview of four monsters including one I wrote.
I've got two original monsters here. Yes, that's only two monstes - but the various templates involved are very flexible, and they have recieved widespread acclaim on these boards...