The right opening song can make or break a movie and forever change the way you think about a piece of pop music. Because there are so many classic examples, we compiled our list of favorites with a few ground rules. First, no musicals -- sorry, 'Sound of Music.' Second, songs only -- hence the absence of the 'Jaws' and 'Star Wars' themes. Finally, directors can only appear once, lest Scorsese and Tarantino completely dominate the countdown. With these guidelines in mind, take a look and tell us which of your favorites we missed.

A "riff" is defined as a short, repeating musical theme that forms a song's framework. Thus, guitar riffs are the basic building blocks of rock 'n' roll -- and we've gathered the greatest of the great. Emotional impact, cultural significance and good old-fashioned recognizability are just as important as being flashy or hard to play. No list of "bests" is going to satisfy everyone, and there's only one song per band, but we hope this will at least get you to go back and listen to some of your favorites. So tell us which riffs rock your world in the comments section, and the best will be featured in a follow-up list.

The rock star film cameo is a time-honored tradition dating back to, well, the birth of rock 'n' roll, but sometimes those guest spots get so much hype they're not really "cameos" at all. (Remember Alanis Morissette as God in Kevin Smith's 'Dogma,' or Keith Richards as Johnny Depp's dad in the last 'Pirates of the Caribbean' movie?) Here are 20 movie cameos by musicians that didn't get quite as much press.

Christina Aguilera's new movie, 'Burlesque,' continues a long tradition, from 'Jailhouse Rock' to 'Purple Rain' to 'The Bodyguard,' of singers starring in films for which they also dominate the soundtrack. Which got us thinking about singers who have defined the sound and spirit of an entire film without ever appearing onscreen. Here are 15 of our favorite examples of singers whose voices alone are like an uncredited main character.

As the "MTV generation" has slowly but surely taken over Hollywood, music geeks have become as common on the big screen as they are in the world's universities, blogs and coffee shops. In the movies, they come in all shapes and sizes -- from the superfan to the pretentious snob to the music-obsessed loner -- but there's a little bit of them in each and every music fan.