There are a few places in town that are still willing to give away pallets and scrap wood.
Pallets are wood platforms used to ship stuff on. Most pallets have a refund, so do not take those nice ones stacked behind stores - they are worth money. Pallets with a 2x4" size frame tend to be all pine, pallets with a narrower frame tend to be hardwood (these are also heavier).
Scrapwood are cut offs and pieces of lumber used for packaging large bundles for shipping. Depending on where the shipment came from the lumber could be hardwood, but most are low grade pines. Packing lumber tends to be pretty beaten up, and most often has routed channels to keep the metal packing straps from slipping.
Agway Ithaca on route 13 gives away used pallets. If you do not need real nice ones, and not that many, they're happy to help you out. If you need real nice ones (hardwood etc) they might ask for a few bucks.
A business on the corner of route 13 and Green Street leaves pallets out on the grass between the sidewalk and the street on a fairly regular base. It's the business with the chain link fence, before Pegasus. First come first serve, obviously.
Cayuga True Value Lumber on 801 West State Street (rt 79 west) has lengths of scrap wood and sometimes pallets for free. The scrap wood is piled up in a small wooden shed off the parking lot on the side of the store - but ask for permission first, sometimes the employees store stuff there for other projects.
Lowe's Ithaca at 130 Fairgrounds Memorial Parkway has a scrap wood bin in the back of the building, behind the saw apparatus in the wood department. They also have pallets on and off. It is a good idea to verify with an employee you have the right bin, the cash register people know about scrap wood being free. I heard about a storage trailer for free pallets parked back there but have not located it yet - ask and maybe you will!
It has become difficult to find decent pallets, especially in winter (wood stoves) and spring (maple syrup). It pays to keep your eyes open! If you find a new location let me know and I'll be happy to add it to the list.