If you style text as much as I do in TextEdit, Mail, and maybe a few other applications, you will probably find this useful. When viewing the Fonts palette (Command-T or Format -> Show Fonts) in certain apps (i.e. TextEdit), clicking on the "Recently Used" Collection will display specific fonts you have used recently -- including the size, color and style.
This can come in pretty handy if you consistently style text in particular ways across applications, and want to keep those styles in reach.
[robg adds: If you have a favorite style that you'd like to have permanently available, click on it in the list of recently used fonts, click the Gear icon at the lower left of the window, and choose Add to Favorites from the pop-up menu. You can't, however, add a specific font with its size and style info to a normal collection; it will add the entire family and lose the color/size info. And yes, this is a somewhat obvious hint, but the fact that it works across applications is quite handy, and not everyone may be aware that the Recently Used collection maintains specific size, color, and style info.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20041212152127871