Acacia	These trees are in the same family as mesquite. When burned in a smoker, acacia has a flavor similar to mesquite but not quite as heavy. A very hot burning wood.
Alder	A delicate flavor with a hint of sweetness.  Goes well with salmon, fish, seafood, pork, poultry, and light-meat game birds
Almond	A sweet smoke flavor, light ash. Good with all meats.
Ash	Fast burner, light but distinctive flavor. Good with fish and red meats.
Apple and Cherry	Slightly sweet fruity smoke that's great with poultry (turns skin dark brown), or ham.
Apricot, Plum, Peach, Nectarine	Great on most white or pink meats, including chicken, turkey, pork and fish. The flavor is milder and sweeter than hickory.
Birch	Medium-hard wood with a flavor similar to maple. Good with pork and poultry.
Cherry	Slightly sweet fruity smoke that's great with chicken, turkey, pork, ham, and beef.
Cottonwood	It is a softer wood than alder and very subtle in flavor. Use it for fuel but use some chunks of other woods (hickory, oak, pecan) for more flavor. Don't use green cottonwood for smoking.
Crabapple	Similar to apple. Provides a lot of smoke. Rich and fruity. Good with poultry, red meats, game and lamb
Grapevine	Tart. Great on most white or pink meats, including chicken, turkey, pork and fish. The flavor is milder and sweeter than hickory.
Hickory	The most commonly used wood for smoking. Sweet to strong, heavy bacon flavor. This great flavor works well with pork, ribs, hams, poultry, and beef.  These chips should soak 1-2 hours to prevent a bitter taste.
Lilac	Very light, subtle with a hint of floral. Good with seafood and lamb.
Maple	Mildly smoky and sweet. Mates well with poultry, ham, cheese, small game birds, and vegetables.
Mesquite	Strong earthy flavor. Good with beef, fish, chicken, and game. Smoke will turn from tangy to bitter over an extended cooking.  Not everyone enjoys the taste of mesquite.  Burns very hot.  Recommended for grilling, but not smoking.
Mulberry	The smell is sweet and reminds one of apple.
Oak	Most versatile of the hardwoods blending well with most meats.  Especially good with beef brisket. RED Oak is good on ribs, WHITE Oak makes the best coals for longer burning.
Orange, Lemon, Grapefruit	Produces a nice mild smoky flavor. Excellent with beef, pork, fish and poultry.
Pear	A nice subtle smoke flavor. Much like apple. Excellent with chicken and pork.
Pecan	A mellow version of hickory.  Works especially well with poultry, beef, pork and cheese.  Pecan is an all-around superior smoking wood. Burns cool.
Walnut	Very heavy smoke flavor, usually mixed with lighter woods like almond, pear or apple. Can be bitter if used alone. Good with red meats and game.

Some sources have recommended that you DO NOT USE pine, fir, spruce, redwood, cedar, cypress, elm, sycamore, liquid amber, lumber scraps, furniture, oleander, China berry, Osage orange, poison oak, wild cherry, shipping pallets, and wood with mold and fungus.  Note:  I have not researched to validate these claims.