iTunes 7 split the library up into various sections: Music, Movies, Podcasts etc. However, I find that it's sometimes useful to see every item in your library in one place. To do so, create a smart playlist with the following rule:size is greater than 0MB.
I named this playlist Everything. Now I can see audio, podcasts, movies, PDFs, etc. -- the entire contents of my library, in other words -- in one place.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20061219050509756