I don't know, Seishirou and Subaru get pretty explicit (in a fun, stabby, angsty way...)...CLAMP doesn't do yaoi, but they're famous for hinty BL-ness. Like Touya and Yukito in CCS, or like EVERYONE in Gohou Drug.
Anyway, It's been a while since I bought anything but I'd suggest...
Vampire Game: If you like comedy and splattering bits of romance. It gets kind of dark in some areas but it's fairly enjoyable. I mean, the idea of a vampire king getting reincarnated in the form of a cat (after trying to take for world domination out of boredom) if pretty amusing in it's own right.
Alice 19th: I'm usually kind of iffy towards Yuu Watase's stuff (I collect a few like Fushigi Yugi and Ceres but not things like Perfect Boyfriend or Midori Days) because the heroines make me want to gag but A19 has a good story and cast to go along with it. The idea of the power of words was actually pretty interesting.
Cain saga: Officially it has 13 volumes, the first 5 apart of the "Count Cain" part and the last 8 apart of Godchild (which she wrote several years later so there's a difference in art style). Warning, there is generous amounts of blood, gore, mind ****s, mystery, and gothicness. It starts kind of slow (and art's kind bland) but then starts speeding up around volume 3 and really grows. If you like mystery and mind games you'll probably like this.