Just want to say this is an awesome question you ask, and I'm really enjoying reading the responses!
That aside, here are my contributions.
Canonically, I think the ones that make the most sense (aside from the ones implicitly mentioned, like James/Lily or whatever) are:
Het: Ron/Hermione, Harry/Luna, Colin/Ginny, Lord Voldemort/Bellatrix, Remus/Tonks Slash: Severus/Lucius (in the 70s), Lord Voldemort/any of his Death Eaters, Dumbledore/Severus, Sirius/Remus, Sirius/James, Seamus/Dean, Lucius/Draco, Fred/George
The ones I think are least plausible:
Het: Draco/Hermione, Draco/Ginny, Severus/Hermione Slash: Sirius/Harry, Severus/anyone he hates (at least in the here and now) plus any interspecies stuff (especially people paired with house elves. ergh. Remus doesn't count in this category. Hagrid only sort of does.)
I'm sure there are more, but it's Friday and I'm braindead.
no subject
That aside, here are my contributions.
Canonically, I think the ones that make the most sense (aside from the ones implicitly mentioned, like James/Lily or whatever) are:
Het: Ron/Hermione, Harry/Luna, Colin/Ginny, Lord Voldemort/Bellatrix, Remus/Tonks
Slash: Severus/Lucius (in the 70s), Lord Voldemort/any of his Death Eaters, Dumbledore/Severus, Sirius/Remus, Sirius/James, Seamus/Dean, Lucius/Draco, Fred/George
The ones I think are least plausible:
Het: Draco/Hermione, Draco/Ginny, Severus/Hermione
Slash: Sirius/Harry, Severus/anyone he hates (at least in the here and now)
plus any interspecies stuff (especially people paired with house elves. ergh. Remus doesn't count in this category. Hagrid only sort of does.)
I'm sure there are more, but it's Friday and I'm braindead.