PDF
A document sharing format created in the early 90s. It is best for highly formatted content and has the ability to use Digital Rights Management (DRM) such as Adobe Digital Editions.
EPUB
An open ebook standard created by the International Digital Publishing Forum (IDPF). It features reflowable text, inline images and the ability to use Digital Rights Management (DRM) such as Adobe Digital Editions.
MOBI
A format primarily designed for PDAs and older mobile devices
AZW
Amazon's propietary DRM restricted format.
LRF
LRF, LRS, LRX are Sony's proprietary formats. They have been superseded by Sony's acceptance of epub as the default format in their ebook store.