Architectural: https://www.m3corp.com/a/download/plans/buildings/
Land, air, and sea vehicles (huge selection of cars):
https://www.suurland.com/
People (warning links does have nude imagery):
https://www.fineart.sk/
For creatures, I recommend you look for tutorials on the type of creature you want since they might include the references for the tutorial.
AIM: mhcannonDMC
"If you love your job, you'll never work another day in your life."