If you liked the Sayonara Zetsubou Sensei anime, the Anime-Planet community thinks you'd like:
Satoshi Yabe is the newest employee at Kamohashi Elementary School. Wide-eyed and enthusiastic, he’s thrilled to finally be fulfilling his dream of being a teacher – but little did Satoshi know that he’d be assigned to class 6-3, a group that houses none other than the violent and perverted Marui triplets! Between the girls trying to hook him up with the busty school nurse, dealing with the unfortunate consequences of a hamster named 'Titties' and other misadventures, Satoshi’s dream of an uneventful school life has come to an end!
Both anime about characteristic pupils and a teacher with problems. Similar jokes and characters. Both really uniqe. The one difference I think is about one is in the middle school and one in primary school. Comedies with little sexual contects.
Negi Springfield is a typical ten year-old Welsh boy -- except that he's a mage, and an English teacher at an all girls school in Japan! In order to become a full mage he has to prove himself as a teacher and find suitable partners to aid him; but above all, he has to make sure that no one discovers his secret. Much to his dismay his secret is discovered on the first day by one of his students, Asuna. To prevent Negi from being punished, Asuna agrees to become his partner -- however she isn't the only one to find out. As time goes by more of his students find out his secret. How long can he keep his powers hidden when little by little all of his students are becoming his partners?
Layered with innumerable in-jokes and tailored to appeal to the fans Negima!? and Sayonara Zetsubou Sensei are part of the current fad for anime that speak directly to the more knowledgeable anime fans. Sharing the ubiquitous "in-joke" blackboard writings that are also a mainstay of Paniponi Dash!, and with the same constant verbal references as Lucky Star, these anime practically require a college-level course in Japanese popular culture and anime to understand. But if one of these is your thing, then it's likely that you'll enjoy the others, too.
Koyomi Araragi can't stop thinking about Tsubasa Hanekawa, the brilliant-yet-modest class representative who always follows the rules, but what the boy doesn't know is that beneath her facade, Tsubasa harbors an extraordinary amount of pent-up stress. Things change one day for the girl when she encounters a supernatural feline that allows her to break free from her normal self... causing immense chaos in the process! Luckily for Tsubasa, Koyomi will do anything to help a friend and he sets forth on a mission to return her to normal by any means necessary, leading to an unforgettable Golden Week.
After Shinbo came to Shaft, their animating style became almost religious, and since both anime come from studio Shaft, they share the same overal feel. Both are funky and bizzare to boot. But biggest similarity would definitely be the comedy.
If you enjoyed one for any of the mentioned, then you could also check out the other one.
Everyone around Kousaka seems to adore cats, but due to his allergies the teen can’t stand them. So when he wakes up one day and can hear what every feline is saying, Kousaka is annoyed to say the least. His new “gift,” it seems, is the result of accidentally breaking an enshrined statue of a cat; and what’s worse, Kousaka must atone for his sin and appease the vengeful spirit by aiding one hundred kitties-in-distress, or become a furry feline himself! Now, amidst helping various cats with mundane and trivial issues, Kousaka must try to dispel the jinx and attempt to salvage his self-respect – not to mention his love life - along the way.
This probably seems out of place, but I recommend Oniinokoto if you liked Sayonara Zetsubou Sensei and vice versa, because both feature forms of the same humor, how Oniinokoto is far more perverted you can expect to see random things like Stalker Chains in both of them, this recommendation may not hold out, but hey, give it a shot.