BibTeX style types.
Source: http://en.wikipedia.org/wiki/BibTeX

article
An article from a journal or magazine.
Required fields: author, title, journal, year
Optional fields: volume, number, pages, month, note, key

book
A book with an explicit publisher.
Required fields: author/editor, title, publisher, year
Optional fields: volume/number, series, address, edition, month, note, key

booklet
A work that is printed and bound, but without a named publisher or sponsoring institution.
Required fields: title
Optional fields: author, howpublished, address, month, year, note, key

conference
The same as inproceedings, included for Scribe compatibility.

inbook
A part of a book, usually untitled. May be a chapter (or section or whatever) and/or a range of pages.
Required fields: author/editor, title, chapter/pages, publisher, year
Optional fields: volume/number, series, type, address, edition, month, note, key

incollection
A part of a book having its own title.
Required fields: author, title, booktitle, publisher, year
Optional fields: editor, volume/number, series, type, chapter, pages, address, edition, month, note, key

inproceedings
An article in a conference proceedings.
Required fields: author, title, booktitle, year
Optional fields: editor, volume/number, series, pages, address, month, organization, publisher, note, key

manual
Technical documentation.
Required fields: title
Optional fields: author, organization, address, edition, month, year, note, key

mastersthesis
A Master's thesis.
Required fields: author, title, school, year
Optional fields: type, address, month, note, key

misc
For use when nothing else fits.
Required fields: none
Optional fields: author, title, howpublished, month, year, note, key

phdthesis
A Ph.D. thesis.
Required fields: author, title, school, year
Optional fields: type, address, month, note, key

proceedings
The proceedings of a conference.
Required fields: title, year
Optional fields: editor, volume/number, series, address, month, publisher, organization, note, key

techreport
A report published by a school or other institution, usually numbered within a series.
Required fields: author, title, institution, year
Optional fields: type, number, address, month, note, key

unpublished
A document having an author and title, but not formally published.
Required fields: author, title, note
Optional fields: month, year, key