Follow the Leader/Anime and Manga

The surprise success of the manga Love Hina, a story about a loser who through hard work, learns martial arts, becomes successful, slowly wins the women in his life, and finally gets to marry his first love. This gave rise to a ton of Harem Series where a loser meets several women who immediately fall in love with this loser for no clear reason.
- It was so bad, that when Ken Akamatsu, the guy who made Love Hina, went to make his next series, they wanted him to make another Love Hina. He agreed - for all of two to five volumes, that is...
Super Robot Genre shows like Tetsujin 28 already had their own success, but it was Mazinger Z that solidified the concept of piloting a robot (via a cockpit within its head, rather than remote control) and started a revolutionary trend that attracted toy makers and captivated children. Such influence would eventually lead to all sorts of landmark works that keep the said genre alive and relevant to this day.
- Getter Robo was the first Combining Mecha and Raideen -almost- was the first Transforming Mecha. Both concepts have been imitated, subverted, ripped off, deconstructed and reconstructed countless times since the seventies by countless mecha shows.
- Mobile Suit Gundam started another trend in the Humongous Mecha shows, creating the so-called Real Robot Genre and being imitated by dozen of shows, mainly in The Eighties.
- Neon Genesis Evangelion has imitators of its mind-screwness, its meaningless religious imagery, its mecha designs, its mixture of pretty girls and sci-fi action, and of individual characters. Examples include Gasaraki, Bubblegum Crisis Tokyo 2040, Brain Powerd, Argento Soma, Fafner, RahXephon, and to a certain extent Martian Successor Nadesico.
- An interesting subversion of this comes from King of Braves GaoGaiGar. While a lot of Super Robot series following Evangelion tried to copy its style, whether it be in character drama or enemy designs, GaoGaiGar was almost a violent throwback to the genre's roots drawing much from Getter Robo, Mazinger Z, Kotetsu Jeeg and the like, it has since left its mark on the genre, helping to keep the popularity of the Hot-Blooded hero type that such series became famous for.
- Infinite Stratos being a pretty decent hit opened up the market for harem mecha musume titles, with Hundred, Undefeated Bahamut Chronicle and Hybrid x Heart Magias Academia Ataraxia being the most notorious ones. Out of the trio, Hybrid x Heart is the most well liked for the sheer raunchyness it wholeheartedly embraced, making it stand out a bit more from the rest of the gamut.
Sailor Moon inspired a deluge of shows based on the Magical Girl Warrior model that it popularized.
- In the same vein, Fushigi Yuugi practically set the trend for the genderflipped Harem Genre. It also brought Mikos into the mainstream.
Anime was largely an underground movement in the States before the success of Power Rangers, which led companies to look for more Japanese material to localize in 1995, including Ronin Warriors, Sailor Moon, Eagle Riders, Teknoman, and Dragon Ball. The Pokémon phenomenon several years later advanced it further, resulting in the localization of not just more Mons-flavored shows, but also the Shonen genre in general. American TV producers have tried to cash in on this as well, but, not wanting to pay for an existing series, create their own. For proof that this rarely ever works out, look no further than Dragon Booster.
while, Mobile Suit Gundam was the first of the Real Robots, it has since set the stage for every Real Robot show to follow from Armored Trooper VOTOMS to Exo Squad to BattleTech.
The success of The Animatrix paved the way for direct-to-video anime anthologies of popular Western franchises, animated by different well-known studios. So far, Batman got in the act with Batman: Gotham Knight and Halo with Halo Legends. Dead Space and Dragon Age has also followed suit.
Samurai Deeper Kyo has been regarded as an imitator of Rurouni Kenshin.
Utena now has at least one imitator, Shitsurakuen. It's about a tomboyish young girl who gets accepted to an exclusive private school and wears shorts instead of a skirt with her uniform (although they came with the uniform, to her confusion). She sees herself as a knight defending the oppressed girls of the school, who are used as weapons/objects by the boys, especially the head of the student council. There is much Ho Yay and Les Yay to be had, too. At least here there's a sci-fi reason for the weapons coming out of the girls' chests: the whole campus is a 3-D stage for a video game.
Dragon Ball's impact on Shonen manga is, well... impressive — to say the very least, its influence now impossible to not see in almost any work in the subgenre. Although not the first employ the vast number of the tropes its most associated with, it became the de facto face of them. To this day, Shonen, and various Anime in general that use elements from, pay homage, or parody, this series and continue its legacy. For proof, one need only look as far as these three anime — often considered the most current and direct of its spiritual successors: Naruto, One Piece, and Bleach.
Cowboy Bebop has spawned several impersonators, notably Black Cat.
Grenadier follows Trigun almost to the letter.
Name a Schoolgirl Series. Name one that isn't at least inspired, if not outright copied, Azumanga Daioh.
Girls Love series in recent years have taken a lot of inspiration for Mariasama ga Miteru. To specify a lot of them have lots of blushing, are set in an all-girls school (often Catholic), feature a Sempai-Kohai dynamic, and are rather like the Romantic Two-Girl Friendship trope. There have been a fair share of parodies though, such as Maria Holic.
Ghost in the Shell, together with Akira, was a massive influence on the later Cyberpunk genre, and inspired several futuristic action/sci-fi works such as The Matrix and Perfect Dark.
Shakugan no Shana is about a flat chested Tsundere that treats the hero like dirt, but gradually falls for him. It popularised very similar stories and characters.
Dr. Slump has a follower of sorts in "Cybot Robotchi" AKA "Robby The Rascal". Both feature a horny, awkward Bungling Inventor with a Punny Name living in a small town in the middle of nowhere populated by weird people and animals, who creates a robot with huge powers but the mindset of a kid (and a lot of other silly and bizarre inventions). Hilarity Ensues, etc.
In 2006, The Melancholy of Haruhi Suzumiya was made into an anime, and its episodes were aired out-of-order (in order to compare earlier and later stories). In 2007, it took some searching to find an anime where the episodes were not aired out-of-order.