Hanaya no Nikai de
This is part of a series, but apparently it works as a stand alone, too. It's tagged as shounen ai, so there's probably no sex, but apparently it's a realistic and deep portrayal of a couple's relationship (aside from the no sex).
The Bedroom Girl, The Sculpture Room Girl
Wow!! How can an 8? page long manga mess me up like that? So powerful! It's the first time I've given 5 stars.
Zankoku Na Kami Ga Shihai Suru
This sounds really good , (though good isn't really the right word here), but it's seriously long, so it'll have to wait. Edit: I just realised this is by Hagio Moto! That settles it then, I really MUST read it!!
Kootetsu no Hana*
Only a hint of shounen ai, but it's not for that that I want to read it.
Baraou No Souretsu
Based on Shakespeare's Richard III. Sounds and looks pretty good.
Coponicus No Kokyuu