As a designer you build a collection of fonts to be prepared for every challenge you may encounter. Every graphic that involves text needs a font and the more fonts you know and the more for professional use you have in your toolbox, the easier it gets to master your objectives!
I’d like to share a few repositories with you, where I find great typefaces and where you can learn more about fonts.
Everybody knows dafont.com, but only very few fonts are available for commercial use and meet the desired quality.
There are great sites where you really can further your knowledge about fonts or use them as a web compendium about the topic.
Different graphics about what parts the letters are build of are graphically executed by Morowolf on deviantART with his piece Typographic Anatomy. Another wallpaper with is more detailed can be found here by font.is.
Typedia is an attempt at an overview about fonts and different types. Especially the page about anatomy of typefaces is great and well illustrated.
Type.it for characters from foreign languages, without having all the keyboard layouts locally all the time.
Readability, a free readability tool for every website.
CSS3 @font-face generator by font squirrel (self-explaining title ;))