When you're working on a document where it's necessary to change fonts (which is probably most of the time), it's always a good idea to keep your favorite fonts readily available. In my case, I have about 800 fonts total in my font library, and it can be a pain to find (or even remember) my favorite fonts while still maintaining a large collection to choose from.
Mac OS X has a great built-in font utility called "Font Book". Font Book is for fonts what iTunes is for music. Just like you can create various playlists for your favorite music, you can use Font Book to create font collections of your favorite fonts (and font families).
To begin organizing your fonts, open Font Book (Applications > Font Book). Upon opening, you will see a list of all the fonts you have installed on your system (including system fonts and fonts that you have installed manually).
To create your own font collection, click on the [+] in the lower left-hand corner:
Once you have created your new font collections, you can search for your favorite fonts and drag/drop them into that font library. When you're done, your list may look something like mine:
Now that you're organized, it's time to start using them In this example, I will use Pages (Apple's word processor app). I have text in the document that I want to change the font for. I simply highlight the text, then press Command+T to open the font chooser (or Format > Fonts > Show Fonts).
The font chooser will allow me to browse my font library by font collection. This makes formatting your documents so much easier than a single, massive list of fonts.