Whether it’s airing “This American Life” tales to half a million downloads weekly or transmitting stories directly to USF, the podcast format has widely expanded since its introduction in 2004.

For students, the right podcast can provide easy entertainment or education while commuting to campus or exercising at the gym.

Yet, with thousands to choose from, newcomers may not know where to begin, much less how to develop a collection.

The Oracle chooses the best free podcasts from four different categories.

Comedy

Comedians have perhaps thrived the most on the podcast format, as they create their own shows and appear on others in a continuous comedy cross-section.

“Comedy Death-Ray Radio” centers on former “Mr. Show” actor Scott Aukerman’s hilarious joke riffs with guests like Zach Galifianakis and “The Pod F. Tompkast” host Paul F. Tompkins.

The two-hour “Top 10 of 2010” episode offers a good entry point with highlights like Tompkins’s John C. Reilly impression and Seth Morris’s Bob Ducca character. Yet, last week’s episode also featured an illuminating and straightforward interview with Pee-Wee Herman alter ego Paul Reubens.

“WTF with Marc Maron” follows a similar format as Maron probes comedians and personalities for an hour with deeply revealing results, including questioning Carlos Mencia on his alleged joke stealing and chatting with Paul Krassner on early counterculture.

The podcast also has a free iPhone and Android app, which makes it even easier to access on the go.

Storytelling

Because of the direct approach of putting on headphones and silencing everything but one person’s voice, podcasts have worked well for storytelling groups like “The Moth” and “This American Life.”

“The Moth” compiles traveling live story recollections that rarely stretch over 15 minutes, but are free and almost always involving.

Celebrities like Run DMC rapper Darryl McDaniels and actress Janeane Garafalo have talked, while many of the most potent, poignant stories come from smaller names – like Anthony Griffith’s story Monday about losing a 2-year-old to cancer.

Though it’s long been known as a radio show, “This American Life” also usually ranks as the week’s most popular podcast. Each episode chooses a theme divided into acts and several guest speakers.

For instance, Monday had the topic of ordinary people saving the day, like author Luke Davies’ story about trying to help someone bitten by a tiger snake in a theme park.

Music

Listening to music podcasts when your own music library is just a click away might seem pointless, but the best programs provide the chance to discover new songs and artists.

“NPR: Live Concerts” offers full, free concerts from musicians like Tom Waits, Radiohead and The New Pornographers, as well as smaller acts that can span two hours.

Last week’s South by Southwest festival in Austin resulted in a particularly large amount of concert content such as showcases from new bands like WILD FLAG and a two-hour show by indie-folksters Bright Eyes.

Indiefeed’s seven podcasts take a different approach by post one new song about every week in hip-hop, dance, indie and blues categories, providing a chance to find a new favorite song.

If you’re looking for something even more alternative, “The Razorcake Podcast” transfers the punk and indie music magazine into a podcast show with well-chosen track lists each week.

USF

Students can even find podcasts that cover their own campus, especially if they look toward the college-related podcast offshoot iTunes U.

Broadcasting station WUSF offers audio and video podcasts of its “University Beat” series, with recent stories including sports concussion summits and solar house competitions.

iTunes U, meanwhile, offers audio of classic literature, such as “Crime and Punishment” and “Moby Dick,” that students can download for free in individual chapter-like podcasts. Other materials include “talks @ USF,” a new collection of campus lectures with video.

There is even “Podcasting-Tech-Ease: Classroom Tech,” which collects several short videos that help teach others how to record their own podcasts.