Snapedom

I think Snupin was among the first non-canon ships I read, back in the day. Definitely the first I read where the people being paired were two that are portrayed as hating each other in canon. I can see how the two of them have a lot in common, however the more I think about Remus' behavior in canon the less I like him and the less I can find it believable Severus might like him - unless Remus starts taking responsibility for managing his condition and behaving more responsibly, growing some spine in general. In a fic where both of them survived the war I can see them eventually getting together, but not before much change.

As for other slash fics, I find Snarry very attractive to read because it is an opportunity for Harry to see canon events from a different POV and for Severus to show his caring side openly.

Severus/Lucius - since Draco was conceived in late 1979 there is also the possibility to fit that ship in before Lucius married Narcissa, if one insists.

I agree Severus has been paired with almost any canon character, male or female on either side of the war. In addition to the above, of the slash pairings I think Draco, Regulus and for some reason Sirius are high in popularity. I have also seen interesting possibilities with Bill. For a while I sought out Severus/Albus fics (there weren't many of them around) but by the time Albus became canonically gay I could no longer stand him and the only way I can see this pairing happening is in a dubious-consent situation with some Stockholm Syndrome. While I can believe that of Dumbledore I'd rather not see Severus in such situations.