Prior to iTunes 9, the iTunes folder structure in Finder had your movies, TV shows, etc. folders buried amongst the music. iTunes 9 allows you to enable sorting such that these all appear at the root of the iTunes Music folder. (That is, open your iTunes Music folder and you will now see folders for Audiobooks, iPod Games, Mobile Apps, Movies, TV Shows, Music, Ringtones, Voice Memos, etc.).

Please note that iTunes will reorganize your files, and you may find some orphaned folders that didn't quite fit into iTunes' organization scheme (it may also add a string of leading numbers to a music file's name in some instances).

Go to File » Library » Organize Library, and then click the Upgrade to iTunes Media organization check box. Once you've done this once, you won't have to do it again (and, in fact, the option will be grayed out).

[robg adds: Note that if you do this -- which I've done and recommend -- it will cause your next music backup (via Time Machine or other backup app) to potentially take a long time, especially if you have a large iTunes collection. In my case, it led to a 67GB Time Machine backup on the next run.]