There are a lot of spinoff manga versions but the main series is this one
http://www.mangaupdates.com/series.html?id=79. According to Mangaupdates the series is 14 volumes total.
There is currently 4 3-in-1 volumes reaching all the way to volume 12. (1-3, 4-6, 7-9, and 10-12)
The single volumes are all the way up to volume 13 but most of them (around volumes 2-9) are out of print.
No idea if they are going to release the final 2 volumes as a 2in1 or just release the final remaining volume as a single volume. I don't have them yet but I plan on buying the 3in1 because of the better quality, bigger size, and color pages.
The rest of the manga series are spin offs.
This post was edited by LyZeR on Apr 9 2014 08:22pm