Nickelodeon is bad with this as a rule, but the fourth season of iCarly takes the cake.
Season 3 managed to air 18 or so episodes (with some double length episodes) in about 6 months. Season 4's season opener was aired in July 2010, and did not finish until almost a year later in mid-July 2011. The season has 9 episodes only, with one double length episode and a 3 part crossover.
The show was budgeted for 13 episodes (which ended up as 8 single and 1 two-part episode that makes up 9 episodes), but the 11th, 12th and 13th were made into a Crossover with Victorious, and basically have the iCarly characters become guest stars on their own show.
And the final episode of Season 4 is a cliffhanger of a sudden Shocking Swerve from one of the characters, and clearly has rushed characterisation due to not having those extra 3 episodes, nor are the fans happy they'll have to wait another 5 months for the first episode of the next season in August to resolve the cliffhanger.
Part of why it's so ridiculous is that, instead of having regular episodes, each individual new episode is treated like a major event, as though it was a special, because new episodes have become so rare!
Power Rangers seems to be catching this from Nickelodeon as well. Samurai/Super Samurai began in early 2010 and didn't end until 2012. One fan crunched the numbers and realized that the 40 episodes of Super Samurai took longer to cross the finish line than the first three seasons of Mighty Morphin (which had over 150 episodes.)
It's not really a case here, as spreading the adaptation over 2 years was the plan all along, so nothing actually slipped. They stuck to the long time pattern of seasons beginning in February and ending in December with long breaks between episodes. Comparing it to Mighty Morphin's schedule is unfair since that was a 5 day a week series, not weekly.
The Sopranos: The first three seasons arrived one per year three years in a row but things changed dramatically after this:
Season 4 was released about a year and half after season 3 which was the earliest example of the fans being annoyed with David Chase's slow plotting pace. Surprise, surprise when season 5 was released a year and a half later. David Chase not being one to settling for that decided he needed nearly two years to plot the sixth and final season. When the damn thing finally premiered it was announced that nine more episodes were added and fans almost had a heart attack when the season actually premiered only ten months later. Say what you will about the controversial ending, most people who had been following the show from day one were probably just relieved it had ended at all.
The Writer's Strike of 2007-2008 caused this for several network TV shows. However, unlike HBO and their fancy-schmancy accommodations and lack of restrictions, network TV is far more strictly regulated in terms of production, airtimes, and the like, so to compensate for the slippage and finish a season up by May Sweeps, many shows had to be cut down from typical 22-24 episode runs (for example, 30 Rock's second season was 15 episodes stretched out from October to May). This had the dual effect of long, frustrating hiatuses during first-run airing and rushed storylines in the actual episode sequence (which are even more noticeable in syndication).
One of the most obviously affected shows was Heroes, and the Strike-shortened second season is usually highlighted as one of the main reasons for its failure.
This also had an enormous effect on the seventh season of 24, as well, which (as one could guess from the title) required 24 episodes per season to fit its plot structure. However, only 8 episodes had been finished by the time of the strike, and, since the show had gotten into the habit of airing its full run of episodes in consecutive weeks, FOX decided to push its airdate by another year. As a result, the first episode of Season 7 ended up airing over a full 19 months after the finale of Season 6. To help compensate, FOX commissioned a TV Movie to fill the gap, airing roughly 2 months before Season 7 began.
Til Death. Besides getting hit by the writer's strike in season two, it was actually pulled from the schedule seven episodes (aired over five weeks) into its third season in the fall of 2008, spent nearly a full year off the air, came back for three weeks in the fall of 2009, was pulled again, marathoned four episodes on Christmas night, spent six more weeks off the air, and finally commenced airing all thirty remaining episodes over four and a half months. Not to mention that the eighth episode of season three wasn't even seen until that Christmas night marathon.
Done on purpose with Breaking Bad. They split season 5 into two parts and broadcast the second part the following year. This gave time for Bryan Cranston to grow a full head of hair, which was integral to the show's plot.
Same thing with Mad Men, also on AMC. AMC realized how successful the last half of Season 5 was, so they followed the same plan.
What was officially the seventh season of 21st-century Doctor Who was split into two halves broadcast in successive years, with a Christmas Episode in between. Despite being supposedly a single season, the second half had a different regular cast and a largely-separate Story Arc. It's widely rumoured that this was because of a budget overspend.
The show's 16-year hiatus is officially classified as this by the BBC, despite both the production staff at the time and the fans recognizing that the show had effectively been cancelled after the conclusion of "Survival."