For yuri, it's a tad obscure, but I highly recommend Strawberry Shake Sweet.
It's beyond adorable, and actually has a realistic main couple, along with some crazy flamboyant side characters. It's one of the best yuris I've ever read.
Yami to Boushi to Hon no Tabibito is also good, although way more fanservice oriented and less realistic.
As for yaoi as a more minor element, as most of the major ones have been mentioned, I'd try anything by Kaori Yuki, particularly Godchild, Nabari no Ou, Kyou Kara Mao, Mirai Nikki, and Axis Powers Hetalia. Actually, I also think no one has mentioned Loveless yet.