I recently took the orientation class. Normally you can't use commercial music like music from iTunes in the production video edits without special permission from the author and probably pay royalties (read: pay $$$$) — but there's another way to get good music in.
It is my understanding that you can use royalty-free materials (depending on license) in a copyrighted work, as a "derived work" if I am not mistaken, I could be wrong.
This will step up your video editing a notch, if there's a little budget for it. (likely on the end-producer's side)
ASCAP, BMG and some other organizations handle music copyrights. *but* there is a segment of the market that is available to commericial interests and recording artists who need background music in their recording but can't produce their own, or need a segment that sounds really cool. They produce what is called "Royalty-Free" music. remember that keyword. Google "royalty-free music" and you'll find a ton. for starters try http://stockmusic.net or http://fotosearch.com
When I want to get royalty-free images for my web site or printed publication for commercial (or whatever) use so (you can sometimes copyright your work too if the stock stuff is a piece of it and not the whole thing), I purchase royalty-free images from a stock image company, such as something like http://fotosearch.com or http://comstock.com and I will purchase their catalog or visit their web site to get them. Images cost about $89-600 for a cd and you get about 40 images on it. Or you can purchase individual images if you are counting costs and only need one from a collection.
Derivative works: some stock photo companies like istockphoto.com don't allow you to create derivative works. So try someone else with different rules if you need to create a derivative work. The copyright office has a document which defines a derivative work.
When I need royalty-free music, I purchase it from a stock music company. When I need royalty-free video, such as the really cool moving-flowing-background series named "Juice" (works great on video titling), well, you guessed it...
Royalty-free music from http://stockmusic.net costs $30/song, is instrumental, has 100 different styles, has a library of royalty-free sound effects (important if you use them), and if you purchase a collection it costs sometimes $149 and you get a lot of songs. Everything from cartoony to electronic, techno to house, jazz fusion, western, dreamy, film trax, you name it, it's in there.
The prices here are just to give you an idea of ballpark costs. Check with the stock resource company for their rules of use.