New Content Countdown Clock

Now that the age of internet is upon us, and cable and satellite have made TV a 24 hour active paradigm, viewers, readers and surfers don't necessarily sit around stuck to one location once they've finished consuming their medium of choice.

Television shows have a finite number of episodes, and when they're out, many channels either fill up the slot with new content, filler, or just play the same episodes over and over again until the new season is ready. When a book is done, there's usually a year or more until the next installment. Web content updates depending on the style of the page.

To drum up excitement and anticipation for the release of new material, popular media will have a New Content Countdown Clock which sits (not at all unobtrusively) in the corner of the screen counting down the hours and minutes until the most anticipated new material.

Particularly Egregious cases (at least in the case of TV) will have the clock fixed in place so that it's even present in the corner of the screen during the commercial breaks.

May often appear—on TV at least—at the end of a Theme Week or Marathon.

Sister Trope to the blurb in the corner that proclaims "new episode!"

Websites

 * Mugglenet has done one for each of the Harry Potter books after the fourth, and all of the movies.
 * Bulbapedia has had one of these for the Japanese and English-language releases of every major Pokémon game.
 * TFWiki.net has done this for Transformers: Revenge of the Fallen and Dark of the Moon.
 * ZeldaWiki did this for The Legend of Zelda: Skyward Sword, with separate countdowns for Europe, America, and Australia.

Live Action TV

 * ABC did it for V when it returned from its hiatus, and also pissed off Lost fans by showing the clock during their show.
 * TNT does this with Leverage.
 * USA had one for Burn Notice. And every new show that's premiered since.
 * Disney Channel did it for the High School Musical movies.
 * A station in Milwaukee counted down the minutes to the Super Bowl during their newscasts when the Packers were in Super Bowl XLV...from the moment they won the NFC Championship. That's 336 hours of countdown time.
 * The Colbert Report website used to do this, with the implication that viewers should be literally counting down the seconds until their next chance to see wonderful, wonderful Stephen Colbert.
 * NBC did it for the Heroes Season 3 premiere during a live hour-long preview of the new season.
 * AMC Runs one every Sunday to the latest episode of The Walking Dead.
 * BBC America has done countdown clocks for:
 * Top Gear's new season.
 * Doctor Who's new seasons.
 * CNN and MSNBC always do a countdown for a big presidential speech; every news channel will also count down to a "polls close" time (or in other terms, for Curb Stomp Battle votes, the time they declare a winner) for an election.
 * ABC NEWS had one counting down to the Royal Wedding of William and Kate.
 * At the end of the preceeding episode of Stargate SG-1, Sky 1 did this for the premiere of Stargate Atlantis. Since they forewent an ad break between the two, and the countdown only occurred over the end credits, nobody minded too much.

Western Animation

 * Comedy Central had one when Futurama was Uncancelled.
 * The Mantis-Eye Experiment, a noted fansite of The Venture Brothers, featured a countdown clock to the first episode of Season 3 once the schedule was announced. I didn't exactly check or anything, but I imagine they did similar for seasons 2 and 4.
 * Cartoon Network has done it for
 * Ben 10 Alien Force
 * The Clone Wars
 * The Clone Wars: Secrets Revealed
 * the premiere of The Looney Tunes Show on screen for the season premiere of Scooby Doo Mystery Inc.
 * the premiere of Firebreather.
 * Nickelodeon has done it for
 * The long-awaited final season of Avatar: The Last Airbender (at least in US markets ...the episodes had aired and the DVDs gone onsale elsewhere).
 * Nicktoons has done it for the anticipated first episode of Dragonball Z Kai.
 * Nicktoons flashed an occasional one to remind viewers of the new Merchandise-Driven Zevo-3 series in the days leading up to its October 2010 premiere.
 * The now-defunct WBKids did the website variation for the premiere of Loonatics.
 * The Hub counts down the premiere of every new episode of Transformers Prime, which has the Autobot logo stare daggers at a viewer while they're just trying to enjoy My Little Pony Friendship Is Magic.
 * Friendship Is Magic itself has this webpage.
 * Green Lantern: The Animated Series has one for the season proper starting in an episode of Ben 10: Ultimate Alien.

Webcomics

 * Homestuck had a quasi-example with its End of Act 5 Animation Bump - Andrew Hussie added a progress bar measured in percentage which he continually updated over the months spent working on it, and partway through issued a target release date of October 25, 2011. Plenty of countdown clocks ensued on fansites.

Web Original

 * Life In A Day did this on their YouTube channel.

Real Life

 * Shops will often do this for when a big product is coming out, such as a video game - often they'll keep a constant clock in the window and just change the images whenever it needs to.