excerpt from Harmony Central
Spruce - Spruce, though not as pretty as maple, is the all-time winner for the "top" of flat top acoustic guitars. According to Fritz, spruce is light and has a tight grain. This enables the wood, when properly cut, to vibrate much like a speaker cone. Better yet, as the guitar ages, the sap hidden in the grain of spruce gradually dries and crystallizes, further accentuating the bright, resonant quality of the wood. "Engleman Spruce," according to Fritz, is the best for making guitar tops.
Rosewood - Rosewood, Brazilian Rosewood in particular, has become the gold standard for the backs and sides of acoustic guitars. Dense and beautiful, rosewood lends a full bass, good high-end bite, and a distinctive "piano-ey" midrange to the tone, according to Fritz. While rosewood is obviously great for fretboards, guitar makers have had limited luck using rosewood elsewhere in solid-body electrics. The guitars are too heavy, too bright, and/or cost prohibitive. This is because the wood is rare and expensive. Plus its porous nature requires a good deal of "pore fill" (and subsequent labor) before lacquer can be applied.
The Martin 00-15 Grand Concert and 000-15 Auditorium guitars with solid mahogany top, sides, and neck.
Mahogany - Mahogany became popular in guitars because it is beautiful and cheaper to get than rosewood. Whereas the high-end Martin D-28 would have rosewood back and sides, the lower-end D-18 used mahogany. According to Fritz, Mahogany lends more of a "parlor" kind of tone to the guitar. In other words, it's twangier but not as brilliant. It's not as "big" sounding either, but possesses a distinct character. This character graced most of the acoustic guitar sounds on early Beatles recordings since they used Gibsons of mahogany construction. As far as electrics are concerned, you can construct an entire guitar (except the fretboard) out of mahogany. The electric tone is marked by a warm sound with lots of low to mid-range frequencies.
Alder - Alder is the classic Stratocaster body material, though the original models were made of ash. Alder is easy to work with because it doesn't require a lot of pore fill. Alder has a full-bodied sound, but doesn't have quite the "bite" of ash.
"It's like the Chevrolet of hardwood," joked Fritz, adding that he sometimes uses alder in semi-hollows too.
Ash - Twangy, porous, and heavy are words that describe ash, the classic ingredient of the Telecaster sound. It also has good bottom end.
"It's an ash kicker," Fritz said.
A flamed maple back
Maple - Maple's two main uses are in necks and as a "cap" on an electric guitar. Maple is extremely hard and dense. While this makes them ideal to support the stress of string tension as a neck, they are too heavy and too bright-sounding for use as a solid guitar body. The Les Paul Standard utilized the maple cap to add brilliance to the body while retaining the warmth of the mahogany. "Figured" maple also adds beauty to the guitar since patterns in the grain can be enhanced in the finishing process. Maple is sometimes used for the sides and back of acoustic guitars, but not nearly as often as rosewood or mahogany.
Ebony - Ebony, when not used in pianos, is a great material to use in fretboards. The wood is extremely strong, bright, and durable. Gaboon Ebony comes only from the Gaboon Province in Africa. It is marked by deep black color. Macassar Ebony is a tad less expensive, and features brown stripes in the black, though it is often dyed to be all black.
Walnut - Walnut is a good alternative to mahogany. It is strong, warm-sounding and naturally beautiful. It works well for solid guitar bodies, and acoustic back and sides. If properly "quarter-sawn" (perpendicular to the wood's annual rings, or a slice down the center of the log), Walnut is stable enough to use in guitar necks as well.
Cedar - Cedar is one of few alternatives to spruce for acoustic guitar tops. Cedar is bright, light, and the deep red color adds a distinctive look to a guitar... plus you won't get any moths in your guitar case!
Though Fritz says you could "go on for days" talking about other "alternative woods," he thought he'd mention the more common ones.
Note: of all the guitars I've had or played (acoustic) Cedar top has to be my favorite, with spruce a close second.
DF