1. You can goto city hall and they can tell you where permits have
been issued for demolition, new construction, remoldeling which are
all good sites.

2. Drive around your city and you can find wood early in the morning
before the the trash man arrives.

3. Construction sites <Home Building>

4. Local city dump

5. Stay in contact with:

5a. City Hall permit office
5b. City Inspector
5c. City dump
5d. General Contactors
5e. Plumbers
5f. Electricans
5g. Tree trimming service
<Bowl turners, Slabbers with 10" band saws or larger>
You can always split the log with a chain saw and let it
dry out, then slab it into useable pieces then rejoin it
back together using biscuits to make wider pieces once
it has been planed & edge joined.

By using up scraps that others throw away we all benefit, why buy a
sheet of plywood when you only need a 12" X 12" piece.

Which makes our money last longer.

David Cooksey

From my experience of working in joinery/furniture/building workshops I can say that just popping in on the off chance that they may have some free offcuts is always worth the while. Especially if you're after a small piece of sheet material. Alot of the time there offcuts that get kept but never ever used again, and for a very small price or free they'll let you have them.
Timber.... generally you will only ever find free firewood in these places though, who knows you could be lucky.... I have seen tonnes of unwanted beading and hardwood offcuts given away in the past.

I pays to become friends with the people at the parks department too. Often they must cut down trees in parks that are dangerous or diseased. After they are down they can be bucked into lenghts and hauled away for milling.