What are the different voice types?

Voice type is a system for categorizing classical and operatic solo singers, and the roles they sing, by the tessitura, weight and timbre of their un-amplified voices in an opera house or concert hall. This classification system is a tool for singers, composers, venues and listeners to categorize vocal properties, and to associate possible roles with potential voices.

The term tessitura generally describes the most musically acceptable and comfortable timbre for a given voice or, less frequently, musical instrument. This often refers specifically to the pitch range that most frequently occurs within a given piece, or part, of music.

Tessitura considerations include these factors: proportion of sudden or gradual rises and falls in pitch - speed of pitch changes; the relative number of very high or low notes; whether lines and phrases of music in the piece tend to rise or fall ¨C the muscular abilities of a singer may be more suited to one or the other direction.

Coloratura describes a style of vocal embellishment, as well as the voices able to perform them.

Female Voice Types:

Soprano

Lyric coloratura soprano ¨C A very agile voice with a high upper extension, capable of fast vocal coloratura.
Dramatic coloratura soprano ¨C A coloratura soprano with a large voice which can sustain fast coloratura at full volume and sing over an orchestra, but does not necessarily have the upper extension of a lyric coloratura soprano.

Lyric soprano - A warm voice with a bright, full timbre which can be heard over an orchestra.
Light lyric - Light lyrics often have a ¡°full package¡± of musicianship, appearance and stagecraft.
Full lyric - Some full lyrics may have a more mature sound than light lyrics, making them less suitable for some of the lighter roles. Occasionally a full lyric will have a big enough voice that she can take on much heavier roles, using volume in place of vocal weight. This is done when a more lyric timbre is desired in an otherwise heavier role. Otherwise full lyric sopranos need be judicious with spinto and other heavy roles to prevent vocal deterioration.

Spinto soprano - It has the brightness and height of a lyric soprano, but can be "pushed" to dramatic climaxes without strain, and may have a somewhat darker timbre. It generally uses squillo to "slice" though a full orchestra (rather than singing over it like a dramatic soprano). It also handles dynamic changes very well.
Dramatic soprano - A powerful, rich voice that can sing over a full orchestra. Usually (but not always) this voice has a lower tessitura than other sopranos, and a darker timbre. - Used for heroic, tragic women of opera.
Wagnerian soprano - A dramatic voice that can assert itself over a large orchestra (over eighty pieces); substantial, very powerful and even throughout the registers. Usually plays a mythic heroine. Successful Wagnerian sopranos are rare, only one or two appear in a generation; arguably there are none singing today.

Mezzo-soprano - A mezzo-soprano's range can be the same as a soprano¡¯s; some mezzo roles call for the "soprano C", but the tessitura is lower. Mezzo voices tend to be quite versatile and able to take on a variety of roles with success.
Lyric mezzo-soprano - A higher and sometimes lighter mezzo voice and can have a range up to or above high C.
Dramatic mezzo-soprano ¨C A fuller and often lower voice than a lyric mezzo; can sing over an orchestra and chorus with ease.

Contralto/Alto

Contralto is the lowest female operatic voice, usually with a deep and dark timbre. True operatic contraltos are very rare. Technically, "alto" is only a separate category in choral music where it refers simply to the vocal range.

Male Voice Types:

Tenor

Leggiero tenor - The male equivalent of a lyric coloratura voice, this is an often light and very agile tenor voice, capable of coloratura and able to sing notes above the tenor C.
Lyric tenor - A strong yet not heavy voice.
Spinto tenor - Heavier than a lyric and more dramatic.
Dramatic tenor - A powerful, rich, heroic tenor.
Heldentenor - A rich, powerful, and dramatic voice.

Baritone

Lyric baritone - High tessitura and lighter voice, quite often a comic character.
Dramatic baritone - Lower tessitura than a lyric, rich and full voice.

Bass-baritone

Bass-baritone - Also called "Heldenbariton", a bass-baritone has the tessitura of a baritone but the lower range that is customary of a bass. Bass-baritones play a variety of roles, and frequently play either villainous characters, or regal older men.

Bass

Basso cantante - Has agility but also a deep tone.
Basso profondo - A rich and deep, extremely dark dramatic male bass voice. Operatic bassi profondi are rare, and these roles are sung by most operatic basses.

http://en.wikipedia.org/wiki/Voice_type provides in-depth descriptions of the different voice types as well as the roles or characters.