If you liked the Zero no Tsukaima (Light Novel) manga, the Anime-Planet community thinks you'd like:
Both series have a main character who is a student of some sort of magic academy and who is considered a failure there. He/she even fails at summoning his pet companion. In both cases the result of the summoning is a human (or something that looks human). In Zero no Tsukaima the summoner is female and her "pet" is male, while in Seikoku no Ryuu Kishi the summoner is male and his "pet" female. In both of those series the female lead treats the male lead like he was her slave. Both series are quite similar, but Seikoku no Ryuu Kishi is way more shallow and way more ecchi, not that Zero no Tsukaima didn't had its share of flaws.
Tsundere meets guy who is more powerful then he seems and basicaly turns him into her salve. Throw in a romantic harem and some ecchi you would swear your reading the other. If you like one your sure to like the other.
Both Zero no Tsukaima and Trinity Seven feature your average Japanese boy being sucked in into a world of magic (though the guy in Trinity Seven doesn't travel through dimensions) and into a magic academy on top of that. Now in this new situation he finds out that he is actually extremely powerful. There is one major difference though, Saito from Zero no Tsukaima isn't cool outside of combat at all (with the few exceptions of showing his cunning side), on the other hand Arata from Trinity Seven can stay cool (almost) all the time. Even though both of them flirt with all the girls in their respective harems, somehow Arata doesn't give of that unpleasant "indecisive male lead" vibe like Saito does. If you want to read something like Zero no Tsukaima, but with cooler male lead, then Trinity Seven might be what you are looking for. Same with Trinity Seven, if you liked it, want to read something similar and don't mind an annoying male lead, then Zero no Tsukaima might just do the trick.