Recyclable wood can come from numerous sources construction waste, industrial waste, pallets, junk furniture, tree trimming, ect.
Lets start with hard woods: More common hardwoods are Oak, Ceder, Maple, Cherry, ect. These woods are ideal for manufacturing furniture and pallets.
Pallet recycling is big business for many companies. Almost every truck freighted item in this country is shipped on a pallet, therefore the market for used pallets and pallet disposal is huge.
Here is a good source for more info on pallet recycling.
Pellet stove fuel: pellet stoves are becoming a very popular alternative traditional wood burning stoves. Generally wood fuel pellets are made from hardwood saw dust ( finely ground wood particles). This material is run through an extruder which compresses the wood particles and forces them thru 1/4" diameter holes the result is small compressed pellets.
The equipment to fuel pellets in low volume is becoming cheaper and there are even some machines advertised on online auction sites for under $2000.00.
Mulch: Wood chip mulch is something almost everyone has seen. landscapers will purchase this material to use for decoration and weed control around trees and shrubs. This can be both hardwood and soft woods. However most landscapers prefer hardwood mulch because it lasts longer.
Softwoods Such as Pine are usually used in building framing and furniture. There is a market to sell this material for the making of wood pulp for paper production.
Some pine and hardwoods from construction waste can be resold as usable lumber depending on it's condition. Many pallet manufactures will purchase used lumber.
Barn Boards: Old barn boards and beams are worth al lot of money. Artists, cabinet makers, and contractors. There is a trend to use these aged timbers in decorative applications.
Just remember that most buyers of scrap wood products require the material to be metal free. So if you choose to get into this market some processing and material seperation equipment may be required.