Hello, South Park! Not only is it one of (if not still) the most dominating show on Comedy Central, but for a time, it was also right beside South Park on TBS for marathon/back to back showings (four episodes in a row!) weekday and weeknight.
CC later dialed back this practice in favor of a similar obsession with Futurama once they picked it up.
On the subject of shows without a huge fanbase, most of the network's time not spent on ponies or Transformers is instead spent on Game Shows.
The Hub also seems to adore Animaniacs, airing promos for the show during every program on the network (even during Animaniacs itself!), and in addition to the Christmas marathon, they ran a two-hour one for Martin Luther King Day (along with The Super Hero Squad Show) and a two and a half-hour one for Super Bowl weekend. Normally, the show airs for three hours on weekdays.
And when The Hub itself was replaced by Discovery Family, the ponies remained, as beloved by the new regime as the old.
My Little Pony has now been upgraded to air 11 times a DAY weekdays on Discovery Family. It has taken 2 of Littlest Pet Shop's slots, and Littlest Pet Shop is the second most aired on Discovery Family. In fact, that's all Discovery Family really airs during the day. During the night, all Discovery Family airs are low rated Discovery Channel originals with little to no promotion.
For those with small children - Caillou on the Sprout network. These are shown in 3-episode blocks 15 minutes in length, and only the first three seasons. This means there are only 25 blocks. Two blocks are shown in the morning, one in the evening (repeated 3 times in the overnight segment), and a full hour is shown from 1-2PM (3 blocks with commercials in between). This means Caillou is shown 9 times a day. There is a 100% turnover of episodes TWICE A WEEK.
As of 2014 it now seems to be Sally Bollywood and Famous Five: On the Case. To wit; both shows air three times a day Monday through Friday (at 7/7:30 a.m., 6/6:30 p.m., and 9:30 p.m./9.00 p.m. respectively)note Famous Five used to air at 10:00 p.m., giving it an extra slot on weekends, but this was changed after a few months, and on Saturday & Sunday at 6/6:30 Oh, and unlike before, where they'd air one episode then rerun it at a later time, it's three different episodes each day. This isn't so bad for Sally, who has 52 episodes, but Famous Five only has half of that, meaning they blow through the whole series in about a week and a half.
As of October 2014, it's now Raggs. Considering that the show has nearly 100 episodes, it's not bad.
The whole time Cookie Jar TV was on CBS, only one show stayed on it's lineup for a long time, Busytown Mysteries. They aired it for one hour every Saturday.
ABC lovedRecess, to the point where it was usually shown twice every week. Not that anyone minded; the show was very popular. Plus, Toon Disney would frequently show marathons of the show (Disney Channel would just show it twice a day) until 2007, when the show was moved up to 9:30 AM every weekday...when the target audience was in school. It remained like this even after the switch to Disney XD in 2009, and was removed in 2010 (and was briefly revived in 2011).
CBS adored Garfield and Friends back at the height of its popularity. After the first season, they showed it for an hour until it was finally cancelled in 1995. Actually, they originally were planning future seasons, but CBS wanted to pay less and less money. It managed to run a year longer than Muppet Babies, the previously Adored by the Network show.
When Teletoon Retro got the rights to Garfield and Friends, they showed it 3 times every Monday through Thursday. As of 2014, the show airs 6 times a day on weekdays.
Teletoon even held a marathon of the show on September 1, 2012, where they showed six episodes back to back from 3:00PM to 6:00PM.
The Latin American Tooncast channel also shows Garfield and Friends for an hour each day like Nick used to do. Also, just like InuYasha is for [adult swim], Garfield and Friends is one of Tooncast's network staples, as it has been airing since 2005. If you count its run on Cartoon Network, where it transferred from, that means it was actually aired for 20 years altogether in Latin America. Due to this, it's not going anywhere soon.
Junior aired the show twice a day ever since it launched until the summer of 2013, when Maya the Bee took its' timeslot.
The Swedish version of Jetix and Totally Spies!. They literally had a programming block called "Totally Jetix": Only Totally Spies, all day, every day.
Polish station MiniMini recently started broadcasting My Little Pony: Friendship Is Magic episodes of both Season 1 and 2 everyday, which amounts to 4 episodes per day from December 2012 to March 2013 (decreased to 3 episodes per day from mid-March 2013 to June 2013 and again to 2 episodes per day from June 2013.).
Fox Kids and Jetix broadcasted all-night marathons of Spanish animation series as Memé Y El Señor Bobo, Mortadelo y Filemón or Iron Kid.
As the page quote indicates, King of the Hill was very popular on FX prior to the syndication rights lapsing. Marathons were common during the early/mid-'00s even without a holiday or other justification.
NBC had this problem with The Smurfs during the 80s, where it was run in 90-minute blocks during its heyday. Nevertheless, it was a huge ratings grab for the network, and it topped even some of the network's primetime shows.
Australian network GO! used to adore Animaniacs, to the point where the Tamagotchi! dub and even Johnny Test were canned for it! It also aired twice in the morning, noon and night.
RTP 2 has had some shows that they wouldn't let off their hands from their kids blocks. This generally applies to co-productions between various other members of the EBU (generally based on the EBU proper). They tried this with Marco and Gina, a show that has been running for over a decade. It's a breath of fresh air when the show is taken off the air, and then, after a while, it returns.
A more recent show, Lulu Vroumette, has been airing on RTP 2 since 2011. It has been airing several times to an extent that they just can't resist in dropping the show. Much like Marco and Gina, RTP partook in this production.
For a good chunk of 2014, the channel aired TeenTitans on weekday slots in a constant cycle. The problem is: only seasons 3 and 4 were airing, until they decided to stop.
Back when Magic Adventures of Mumfie first aired, ANY network that aired it would treat it like a precious gem and make sure they aired it for a very long time or promoted it a lot. Here are a few examples:
ITV loved promoting this show alongside Astro Farm and featured it in all of their combined shows promos.
Fox held onto the Mumfie license for five years across their networks. It got to the point where the normal Mumfie show on GirlzChannel competed with the Mumfie segments on Storytime with Thomas!
Nick Jr. UK ran it for nearly five years twice a day.
KiKa in Germany broadcast Mumfie twice a day and had it for twelve years. It was also one of their highest-rated programs.
In Japan, NHK showed it occasionally after it's initial run up until Kids Station got the rights and lost them in 2001.
The Norwegian broadcaster of Mumfie is a very special case: Much like the Italia 1 Dragon Ball example listed on the main page, the show almost never took a break from airing (save for short ones in between each season lasting anywhere from one week to a month). And it's been going on for almost twenty years. As of late October 2014, they've begun airing the second season again after one of those short breaks.
American Public Television (a syndicator of programming mainly to PBS member stations) has had the rights to Zula Patrol for ten years now, and it seems as if they won't let go of it. They've gone through the same thing with the newer Wunderkund Little Amadeus.
Undergrads, a quickly-cancelled American cartoon on MTV, grew to become very popular in Canada to the point where Teletoon would air it constantly. It aired once a night for years, despite the show only having a tiny handful of episodes. It goes off the network for long stretches now, but is often still trotted out in the nightly run of shows, despite being more than a decade old by this point.
Most, if not all foreign over-the-air TV channels outside of North America that run kids programs will often share a program: Arthur. In a similar manner to The Fresh Prince of Bel-Air, the show is available in exchange for ad time.
HBO Family loves rerunning the series "Storybook Musicals" despite being complete in the late 90's. The series adapts children's stories like The Tale of Peter Rabbit and turning them into a musical.
Same goes for the 1999 HBO Family original movie "The Sissy Duckling" which is a unique take on The Ugly Duckling.