Pita-Ten is a 8-volumes-long series by Koge Donbo, the creator of Digi-Charat. But don't expect tiny girls from outer space in this story.
Pita-Ten tells the tale of a young boy called Kotarou, who has to lead a rather independent life following the death of his mother and with his father often away at work. One day, however, an incredibly energetic and cheerful (more like hyperactive) girl called Misha moves in next door and claims to be an angel. The story mainly follows the relationship between Kotarou and Misha, as the "angel" tries to help her friend out in every way she can, but often makes the situation worse.
As you can probably work out by the art style, Pita-Ten is basically supposed to be an ultra-cute series. The pink-haired Misha often ends her sentences with "-su" and fills silences with a "teeheehee". In the English translation by Tokyopop, the way Misha talks can get rather irritating, as it gets a bit like strange a mix between Texan dialect and baby talk. I'll admit that the first time I picked up this series, I gave up reading by the first volume just because I couldn't stand the way Misha talked. But I'm glad I gave it another chance.
If you have seen the anime version of this (which is unlicensed at the time of writing), I can assure you that the manga series is darker and deeper. The first few volumes just show the characters going on with their ordinary lives, which holds a few funny moment. But if you're thinking it's a bit childish - stick with it. In the later half of the series, it gets surprisingly dark (for a series like this, don't expect anything like Hellsing here) as Kotarou finds out about who Misha really is. Before I knew it, I just kept reading and reading as more things were revealed. That was what made the series just slide up to 5 stars for me.
If you're interested in getting this series, I recommend getting the box-set with the first four volumes. The box itself is just made of thin cardboard, not as good as some of the other Tokyopop boxes, but it works out cheaper anyway. At just 8 volumes long, it's a nice (and more affordable) addition to a manga collection.