It's all about the villains, Dark.
(If you're only familiar with the English dub however, you would remember Zoisite as being female. A very flat chested female... American kiddies can't handle homosexuality apparently.)
As far as popular yaoi in Sailor Moon (though not necessarily canon), Kunzite/Mamoru is popular in manga-based fics, and there is a heck of a lot of Nephrite/Jadeite doujin out there (left overs?). I've seen Demando/Mamoru as well. Oh, I bet Fiore/Mamoru would be big as well, or at least it should be...
Within PGSM fiction (PGSM = live action series 2003/04) there are sadly no canon male/male pairings. Mamoru/Zoisite seems well received though, and the potential power struggle between Kunzite and Zoisite is good too. There was one author who wrote 15 ficlets pairing each of the Shitenou + Mamoru with each other, so ever possible pairing does exist in writing somewhere. (My avatar shows the live action versions of Kunzite (black hair) and Zoisite).