The one I had in mind when I wrote it was Remus/Hermione.
She chose bravery over brains,
Though she could've had either one;
This is illustrating that although Hermione ultimately ended up a Gryffindor, she also had the necessary qualities to be a Ravenclaw.
And I think he's the same--
Noble heart, clever head in one.
Remus is another intellectual sort of Gryff.
If someone forgets his conscience,
One of these two can help him remember.
Both Remus and Hermione have a knack for reminding people (like Harry) about right and wrong.
I'd like this pairing a lot more,
If it weren't so May-December.
I actually do like the pairing just a teeny bit, apart from the cross-gen-ness as mentioned above--and my belief that she belongs with Ron, of course. :)
The other possbile answer is Hermione/Dumbledore, since Dumbly is also 1) a brainy Gryff, 2) good at reminding people about right and wrong, and 3) too old for Hermione.
The House points currently stand thus:
Ravenclaw (angua): 35
Slytherin (meanies): 50
Gryffindor (redwood, veela): 20
Hufflepuff (lilac, piper, points donated by veela in honor of Cedric *sniff*): 25
Just two riddles left to go, though it appears a Slytherin victory is nearly inevitable. Figures.
This next riddle is another Who Am I?
Few are able to find us,
And fewer have sought to bind us.
But there is nothing to fear,
For we have always been near.
I originally wrote it with three couplets, but I thought the first one gave too much away, so I cut it. If this shorter version proves too difficult, I will add the first couplet back on.