Yuuto Amakawa has had a tough life. Seven years ago, both of his parents were tragically killed in a car accident, leaving him without a single living relative. His friend Rinko Kuzaki has taken care of him every since. Yuuto's sixteenth birthday has arrived, but instead of a birthday gift of a normal life he meets Himari, a catgirl samurai who swears to protect him. Within weeks Yuuto's life is thrown into chaos as his family's dark past comes to light. With demons appearing around him, Rinko and Himari fighting for his attention and a sinister plot beginning to surface, can Yuuto live the normal, safe life he wants so badly?
A year after their spaceship crash-landed on Earth, the alien species known as 'DearS' have been accepted into the Japanese citizenry. They are adored by many fan groups and trusted by most humans - with the exception of Takeya Ikuhara. Kind-hearted but resistant to change and skeptical of the DearS' seemingly-friendly behavior, Takeya tries to have as little to do with them as possible. But after he saves a girl from an incoming truck, and she turns out to be a DearS, Takeya ends up being far more involved with them than he could have ever imagined.
These two series are similar in more ways then I would have thought possible. Both are fanservice laden ecchi, both are romance based, both involve a master-servant relationship. While Ren and Himari themselves are very differant, I would definately say if you liked one, you'll like the other.
Both Omamori Himari and Inukami! feature a male lead who is an exorcist of sorts and a female youkai (a dog one in Inukami and a cat one in Omamori Himari) who is his servant. It should be noted that the main duo from Inukami has much more character than the one from Omamoru Himari. Nonetheless you might want to check one of those if you liked the other.
Those series are awfully similar. Both revolve around some normal guy who suddenly finds himself involved with a number of exorcist girls and some youkai (namely a female cat one). Both series go too far with ecchi, but Omamori Himari is the one more guilty of that, On the other hand the characters from Isuca are a considerable improvement over those from Omamori Himari (that doesn't mean they're any good and one can't forget that the female lead from Isuca is a horrible tsundere).
Though less fanservice-tastic and slightly more violent, Kandachime also tells the story of a boy coming to terms with his own power while fighting the supernatural. The predominantly female cast will appeal to readers who liked the harem aspects of Omamori while the slick action sequences will appeal to those who enjoyed watching Himari tear up demons.
Urashima Keitarou is a loser. He's failed the Tokyo University entrance exams two years in a row, and his parents have finally kicked him out of the house. Penniless and destitute, he travels to his grandmother Hinata's inn, hoping she'll put him up until he can get into Tokyo U and fulfill his promise with his childhood sweetheart (whose face he can't even remember). Unfortunately - or perhaps fortunately - it turns out that the inn is no longer an inn... it's an all-girls dormitory, as he discovers in his typical blundering fashion by grabbing an eyeful and more of every girl in the place! Narusegawa Naru, a fiery-tempered high school student and the first victim of Keitarou's lewd bungling, wastes no time doling out brutal punishment and preparing to kick him back out to the street. But wait! A letter has come from grandma Hinata, and Keitarou is to be the dorm's new live-in manager! Is this a blessing from heaven, or has he been cursed to a living hell?