Andy Lykens is a music branding and marketing specialist for indie music publisher Imagem Music. He blogs at andylykens.com.
By far the top question I get from independent musicians about getting their music in film, tv, and advertising is "who do I contact?" Most of the information you need exists online as far as WHO you need to contact. Here's a quick rundown of some GREAT resources.
Advertising - Ad folks are no more difficult to find. Probably the biggest downfall to the ad industry is that the creative decisions might be funneled to a specific music producer but the final say is up to the end-client (the brand) or, at the very least, a group of creatives at the agency. This makes it tough because you can get into the running for a spot, but then at the last minute someone else can come along and veto. It can be a frustrating process if you let it get to you but if you learn to roll with the punches, something will come along. The best place to get contact ideas is AdWeek. It's a cool publication all around if you have any interest in advertising outside of music, but they often post credits for their "Ad of the Day" where you can get names of specific people working on specific brands across the globe.
Video Games - Video games can be a bit trickier, but you have to remember that the people with the coveted positions as music producers and music supervisors have been interviewed, participated on panels, and generally are bombarded with enough attention that digging them up on Google is easy. Give LinkedIn's search a shot, or try Googling the video game company's name along with "music supervisor" and see what you come up with.
People You Know - You probably have heard a million times that the best source of pretty much anything is your address book. I can't emphasize enough that having a connection to someone who can potentially use your music will be the most efficient, least painful way to go about securing a license. Both parties involved will be more comfortable leading to more useful conversations earlier on. Hit up your Rolodex and see if you know anyone that works at an ad agency, in film or TV, or at a video game company. They don't have to be THE music contact, but they will be able to help you in some small way if you ask.
Finding the right people is really straight-forward and easy to do. If you're smart about it, you can put it to use TODAY to start building relationships with the proper folks. I'd like to emphasize "building relationships" and not "sending emails all about how great you are." Keep that in mind before you start dropping emails to folks, they will VERY much appreciate a genuine connection versus yet ANOTHER artist sending them more music they've never heard of and don't care about.