Need a monster that fits your campaign or next adventure just right? Well a ref has an incredible host of monsters to choose from when creating campaigns and stocking dungeons. The original Monster Manual had hundreds and many volumes have followed since for many iterations and emulations of the game (and related games). Online sources such as the pathfinder SRD and the Swords and wizard SRD give ready access to several hundred monsters and different takes on them. Blogs and fan websites offer an incredible array of gruesome grues to populate your game world with. There is no shortage of monsters out there to dig through when making selections for your campaign.
Here’s a list of free monster sources:
Swords and Wizardry SRD https://sites.google.com/site/swordsandwizardry/swords-and-wizardry-srd/for-the-referee/monsters
Pathfinder SRD Bestiary http://www.d20pfsrd.com/bestiary
Monster of Myth (Osric Format) http://www.lulu.com/shop/the-first-edition-society/monsters-of-myth/ebook/product-17452854.html
A Hamsterish Hoard of Monsters http://rendedpress.blogspot.com/2012/07/new-release-hamsterish-hoard-of-monsters.html
Links to Wisdom Monsters http://campaignwiki.org/wiki/LinksToWisdom/Monsters
Telecanter’s Deadly Distractions http://city-of-brass.org/TelecantersDeadlyDistractions.pdf
D20 SRD Monsters http://www.d20srd.org/indexes/monsters.htm
The Basic Fantasy Field Guide to Creatures Malevolent and Benign http://basicfantasy.org/download.cgi/Basic-Fantasy-Field-Guide-r2.pdf
Oriental Monsters A Supplement for B/X http://www.mediafire.com/view/?t49aq05ki7yyey9
A book of wondrous beasts http://engineoforacles.files.wordpress.com/2010/01/a-book-of-wondrous-beasts6.pdf
Varlets and Vermin http://rolesrules.blogspot.com/2010/05/varlets-and-vermin-10.html
What Lies Beyond: the Chapman Bestiary: http://www.flatlandgames.com/btw/downloads/
The list above is incomplete there are other free collections out there and countless blog posts but the thousands of monsters available in the selections above should provide a good starting point. Don’t forget all the clones and simulacrum games that have free versions have lot's of monsters in them too. Happy Monster Hunting !