Blood bank and free kisses .
Every manga by Harada. The one i like the most is Yatamomo, there's lots of sex plus plot.
sakira has nice sex
There are a few I can think of...
All of Zaria works are very sexy, for some good sex you can read hehe.
rAlso one of my fav is Bi No Kyojin from Ike Reibun but it has a very manly mature sex.
Mmm Window to Window is good too! And Blood Bank is a masterpiece.
Also Sachimo's works a very nice with sex scenes too!
I need whatever yaoi you think has the sexiest, most erotic sex scenes .