If you liked the Yamada-kun to 7-nin no Majo manga, the Anime-Planet community thinks you'd like:
Daichi Shinigawa is a typical delinquent who wants nothing to do with high school. However, bespectacled Hana Adachi, the class representative, will do anything in her power to make sure Daichi participates in whatever events the school has to offer. If she has to surprise him in the boy's bathroom to get him to go on the school field trip, so be it! Daichi is confused as to why a class rep would care so much about a troublemaker like him; what could be the reason behind her actions?
Both series have similar setting, style and characters, but that's not surprising considering the fact that both were written by the same person. So, if you liked one of them, you'll love the other one.
Both of these series are written by the same author, and it really shows. The setting, characters and humour vary between being very similar, or totally identical.
Yamada-kun to 7-nin no Majo is the better of the two, it just 'clicks' in a way that Yankee-kun to Megane-chan didn't, but both are very good reads, and anyone who enjoyed one will certainly enjoy the other.
Nothing beats a good school-based comedy with magical elements, and both Kagami and Yamada contain plenty of those with a bit of romance (More prominent in Kagami) and a nice dose of perversion. The magic in both of these series though isn't single-person oriented, as in they need two people for it to take effect. If you have, by some stroke of luck, read either one, check out the other for more of the same style of fun.
Both have their roots firmly dug in the soil of comedy, magic and school adventures with the leaves of perversion scattered about. Mx0 is up and front with it's magic while Yamada-Kun is more human-oriented; without secondary objects needed to conjure up some witchcraft. Their methods are different in that aspect but they share the same branches with their comedic style and secondaries to work some chemistry with the mains. Both may get dramatic once in a while but they're comedies first and foremost. A fan of one would like what the other has to offer.
Both these manga are romantic comedies that follow a male character as a sudden influx of beautiful, and irritating girls find their way into his life. It's a pretty well worn concept, but these two have male lead who is more than just an infuriatingly dumb, and boring archetype we see so often.
The comedy in both is also great, with plenty of fun characters interacting, and conflicting with one another in some pretty surreal circumstances. Nisekoi is grounded in reality for the most part, while a lot of the comedy in Yamada comes from the supernatural aspect of the series. But both are consistantly funny, and i find it hard to believe that a fan of one wouldn't find the other appealing.