Tokyo Babylon, Yami no Matsuei Recommendations
Both series are about protagonists who use their spiritual powers to help the living and the recently deceased. Both also start off relatively lighthearted and gradually get darker in tone, though Yami no Matsuei is a lot quicker about it than Tokyo Babylon. The situation between Subaru and Seishirou turns out to have some striking similarities with the Hisoka-Muraki backstory as well.
Both, at first glance, seem to be funny and fairly light hearted, if a little heavy at times. Upon closer inspection, however, one will find that both have very similar dark undertones that leave the reader wondering if something much more sinister is brewing beneath the surface.
Both also deal with major supernatural and somewhat disturbing elements, in addition to real life drama. Add in the heavy implications of shounen-ai thoughout both of them, and you have two series that are very similar and very interesting!