If you're looking for manga similar to Beelzebub, you might like these titles. All recommendations are made by Anime-Planet users like you!
Yuuhi Amamiya is a loner whose mistrust of people was instilled in him at a young age by his abusive grandfather. So when an annoying talking lizard tells the university student that he is one of twelve knights chosen to stop the gigantic "biscuit hammer" before it smashes the Earth to smithereens, Yuuhi has no inclination to rescue such an unkind world. Despite his apathy, the boy is targeted by a golem while going about his day-to-day life, and ends up teaming up with the other knights anyway. One of his new companions is Samidare Asahina, the "princess" and leader of the knights, who secretly is only trying to protect the Earth so she can destroy it herself! Entranced, Yuuhi swears eternal loyalty to this cheerful devil that promises to crush the world he despises.
In both stories main character is slightly evil guy (vicious deliquent in Beelzebub and scheming guy who can pull any cheap tricks to achieve his goal in Hoshi no Samidare). That "protagonist" is suddenly given a role, where the fate of the world is in his hands (being a parent to demon lord ni Beelzebub, and becoming one of the knights that are suppose to protect the planet in Hoshi no Samdare).
Both mangas are filled with comedy mixed with some battle manga elements. Both are walking a fine line between good and evil ( it's hard to decide on what sides are the characters, since they are pretty likable and do good deeds now and then, while still taking actions that may end in world destruction).
Lastly in both mangas demon lord make an appearance as one of the main characters.
Honoka Sawada is a lonely fourteen year-old girl who has no friends at school and spends her nights alone - that is, until one day she wakes up to find a fire-breathing baby named Mao in her bed! After meeting the mysterious principal of the Chibi Devil nursery, Honoka learns that Mao is in fact a demon baby, and she is now his surrogate mother. With only her anime-obsessed childhood friend Kyou and his hot-headed pal Shin to rely on, Honoka decides she can’t possibly look after a child and asks the principal to find a replacement parent. Now, until a substitue can be found, Honoka will have to spend the next month looking after Mao, but will she be able to cope, especially when a strange pair of teenagers are intent on taking Mao for themselves...
Yuusuke is a street-fighting, class-skipping juvenile delinquent. Killed in an unexpected act of kindness, he thwarts the spirit-world bureaucracy and ends up with a second chance at life... as infant prince of death Koenma's Spirit Detective! Simultaneously cheered on and kept in line by Keiko Yukimura, his childhood friend, he is joined by a spiritually aware human, two demons on parole, and guided by a much too lively ferry girl of the dead. Together they plow through demons, tournaments, hijinks, intense "martial arts" training, cross-dressers, dungeons, conspiracies and bad puns alike. At the end of the day, what's it all for? Kicking butt and saving the world, of course!
Both Beelzebub and Yu Yu Hakusho follow a delinquent teenage boy who is the toughest kid at school. Through different events both protagonists becomes involved with the demon world, and they each aquire some powers. These two are about as similar as two titles can get. They are each totally unique, and if you liked one, you would for sure like the other.