i'd start looking mostly for textures and record at high sample rates, then you can use pitch shifting to manipulate size in post.
You're going to want props that are legitimately old and have loose internal fibers. I'd get some gloves and try looking at recent building demolitions, junk yards, those sort of places. Also, try the craigslist free sections. Sometimes furniture or other wood-based things show up there.
with regards to manipulation - think leverage. Don't be afraid to utilizes some levers and other tools to help with the bending and stressing - especially with metallic things. There are times when your own arm strength just won't be enough, even with small to medium sized props.
Another good way to get creaks is with friction. The right board at a 45 degree angle to another can do all kinds of crazy things.
man, now I want to do some. :)