This is a full index of all articles from the print run of Dragon Magazine, all the way from 1rst edition to late 3rd edition. If you search with words like "ecology" is should bring you to a list of all the monsters done over the years. The monster ecology book for sale from Paizo contains the 3.5 ecologies (and maybe the 3.0, and possibly some new ones, not sure, sorry).
But this should go a ways to getting you started on narrowing down your selections.
The sub-series of Revisited books within the Pathfinder Chronicles line also has ecology-like information.
The sub-series of Revisited books within the Pathfinder Chronicles line also has ecology-like information.
These are great for getting into a monster as a episode's Guest Star. I recently had a new party start off by making peace between a minor goblin race that lived in their city's sewers and the 'horrid man, er, goblin eating' monster at a lower level, an Otyugh to big to escape and desperate for a mate in another part of the sewers. Many references to the Horta where made by the old farts. Don't they require watching ST: the original anymore? kids these days only know Shatner from Priceline commercials!