Fontdeck helps you discover web fonts, you can also preview the fonts on your blogs and websites for free! Once your blog/website is ready, you can go ahead and buy the full licenses
Font Squirrel is a resource for high quality hand picked fonts. It claims to have fonts that are free for commercial use.
MyFonts says that it has the world's largest collection of fonts, that can be true since we found that it has all the latest font on it! It also has an advanced search feature called "WhatTheFont" which helps you identify fonts from a picture you've uploaded.
Da Font is by far our fav! All the fonts on it are free and are share friendly. It even has a ton of demo fonts. It is a well organized site which has fonts ranging from gothic to cursive to handwritten, you can preview fonts with your own text before downloading the file.
Google Web Fonts is a huge directory of all fonts that have a open source license, served by the google servers only.
Typekit is a web service that serves hundreds of website fonts that you can use for your webiste or blog by just adding a line of code. There is a specific price point, but it is worth it!