P22 is an independent foundry specializing in historical letterforms that were previously unavailable in digital format.
MyFonts is a distributor of digital fonts from many type foundries in one easy-to-use Web site. It also includes a useful type identifier, What the Font, that searches for fonts provided for purchase on the site (see type identification).
FontShop is claimed to be the original independent font retailer. They produce the FontFont typeface library and have cutting edge fonts with some European influence.
FontHaus offers useful content, easy font finding features, a huge selection of name-brand fonts, font compilations, and libraries. They have been offering fonts since 1990 and are a popular resource.
Adobe has immensely influenced the evolution of digital type. They offer PostScript, Multiple Master and OpenType formats. Their collection is comprised of many graphic standard types.
Linotype offers quality fonts and is well respected in the design community. They have existed for over a century and have adapted well to new technologies.