The app that I use the most on my current phone is one called BeyondPod. It is, if you haven't guessed, a podcast app. Podcasts are "a type of digital media consisting of an episodic series of audio radio, video, PDF, or ePub files subscribed to and downloaded through web syndication or streamed online to a computer or mobile device." (Wikipedia)
BeyondPod is one of my most used apps for many reasons; chief among them is because I spend a lot of time driving, and I need to be both productive and alert during that time. I find that listening to podcasts is great way to accomplish both of these objectives.
Many people will tell you that they can't suffer a long trip without music. But when you spend enough time driving, the repetition that comes along with a regular radio station is maddening. Radio stations have to play what is most popular in order to keep listeners coming back. Which means they play the same 15 to 20 songs on a reoccurring loop, ALL DAY LONG. Not to mention, when you drive long distances, I typically drive between 35 and 70 miles one way to work, you can drive in and out of radio station coverage, and keeping the constant stream of music flowing can be a hassle. Not to mention the 10 minute long commercial blocks that radio stations need to subject you to in order to remain financially solvent. Call me crazy, but I hearing the same used car dealer prattle on time and time again about how much inventory they have, and their great pricing just doesn't hold my attention.
I also use podcasts to be productive. If you have an interest, hobby, profession or maybe you want to learn a new language, there is someone in the world that produces a podcast for you. In my current profession I need to keep current on what is going on with technology. So my playlist includes: All About Android, MacBreak Weekly, Tech News Today, This Week in Google and This Week in Tech (all from the TWiT network). There are times when I do get "tech'd our" though, so I also subscribe to Freakanomics Radio, and The Moth Podcast, when I want to listen to human interest stories. But you can find podcasts that cover just about everything under the sun from personal fitness to financial management to cooking to sports to music. If there it is written about on the internet, then chances are there is a podcast about it somewhere out there.
BeyondPod is hardly the only podcasting app out there. I have been using BeyondPod for more than a couple of years and find it easy to navigate (because of familiarity) and very functional. There are quite a few podcasting apps in each of the respective operating systems app stores, and in fact iOS, Windows Phone and Blackberry all have their own podcast app built into the operating system. My suggestion is to try out a few and pick one you like. It's free and easy, and like I said, much more engaging and entertaining then listening to "DEALS, DEALS, DEALS!"