I thought I'd be non-traditional for Valentine's Day, so instead of recommending stories about the hearts-and-flowers happy lives of couples I'm recommending stories with threesomes. *grins*  These are some of my absolute favourites from the Harry Potter verse, although there are lots that I've really enjoyed. (And there are one of two stories that I haven't posted because I seem to have lost the links, including a beautifully written Percy/Anthony/Neville short story that was written not so long ago, if I remember rightly, and if anyone could send me a link to that I'd be all kinds of happy.) Trawling through the 'mulitples' tag here on know-it-alls leads to a lot of lovely fic, including links to some of those posted below probably.

So, hope you all have a happy Valentine's Day and a good weekend!

 

Care of Magical Creatures (Adult, novel) by Arsenic Jade
Eventual Hermione/Remus/Severus (past Hermione/Harry/Ron): Hermione stumbles onto her path.
This isn't just one of my favourite threesome stories but one of my favourite stories hands down. It's a long, plotty novel where Hermione takes on the issue of werewolf rights - an issue that is never treated with anything less than it deserves in this fic. The character interactions are amazing, the world-building fantastic, the original characters could be canonical. And there are sequels!

Complete (NC-17, 2,771 words) by heather11483

 Harry/Hermione/Ron: She can't sleep without them there.
Wonderful Trio-fic where everything just fits together, including these three friends, and I love the dialogue, which is so very them.

Scarborough Arithmancy (Adult, multi-chaptered) by lillithj
Hermione/Severus/Lucius (past Hermione/Harry/Ron): Arithmancy has often been defined as the science that deals with the laws of magic. (Elements of Arithmancy, Reichenbach, H. c1947.) Equations, however, factor only what the Arithmancer knows to be true at the time. Sometimes unforeseen circumstances throw a kink in the works. Magic doesn't behave as one expects and solutions can be found in a chance meeting 10 years later.
There are all kinds of reasons why I think this is a great story, from wonderful characterisations to fantastic world-building, but what I love the most is the innovative and detailed magic. Meet the Unfathomables and their Mapparium, and a great plot.

Puzzle Pieces (NC-17, 50,000 words) by Em North
Draco/Hermione/Blaise: All Blaise wanted was some Transfiguration tutoring. What he got instead was a whole new world.
This is my favourite story with this threesome, perhaps because the characterisations are true to canon and yet manage to make this emerging relationship plausible. Perhaps because it's a lovely mix of romance, smut, and plot.

Triangle (PG13, 2,281 words) by holyfant
Harry/Ginny/Luna: It’s a hot, heavy summer evening when Ginny realises for the first time that Luna Lovegood has never lied to her.
This is beautifully written.

To all of us on our way through life (without our noticing for a time) (NC-17, 13,000 words) by fourth_rose
Harry/Luna/Draco: It is four years after the Battle of Hogwarts, and all is not well. Harry Potter, husband, father, and Junior Auror, has everything he ever wanted – which only goes to prove that you should be careful what you wish for.
How these three come together in this story amuses me, as does Luna's matter of fact way of speaking and dealing with things.

Bermuda (Adult, novel) by pigwidgeon32
Hermione/Severus/Lucius: War heroes aren't always treated as they should be. Due to a ministerial intrigue Severus Snape, Lucius Malfoy and Hermione Granger are practically prisoners at a mental institution. But if one Gryffindor and two Slytherins join forces, they're able to overcome almost any obstacle.
Funny with hot moments and dark moments, and a fantastic, fun plot.

Shared Opinions (Adult, 5,232 words) by florahart
Fred/George/Pansy: It wasn't as though there weren't places she could go. Her new life was underway.
The characterisation of Pansy in this is amazingly wonderful.

Three Galleons (R, 4 chapters) by sam_storyteller
Severus/Hermione/Remus: After the war, Hermione has settled into a quiet if unorthodox life with Severus -- until a small problem in the form of a refugee spy calls for an even more unorthodox solution.
The three characters come together in a believable manner with some great dialogue and wonderful storytelling.

And...

Seven Things That Never Happened On Valentine's Day, Or Maybe They Did (R) by glitterati
"This is the weirdest Valentine's Day yet," Peter mused. "But not 'ever,'" Remus said dryly.
Okay, so this isn't a threesome fic, but no Valentine's Day would be complete without this fic of hilarity with the marauders. :o)