Harry/Ron/Draco
"The Malfoy Guide to Productive Extortion" by Mirabella NC-17 -- Harry's either drunk and horny or drunk and cuddly, depending on your point of view. Ron's straight but no one holds it against him. Draco could hand out detentions, but he has a better idea.

"Suspicious Seasons by emcue PG-13 -- Two pairs of want, two pairs of need.

"Tempting Fate" by Ivy Blossom NC-17 -- Threesomes have consequences.

Harry/Draco/Ginny
"Enter the Heroine" by Marks NC 17 -- It was a dark and stormy night. A scream echoed in the corridors! Ginny goes to the rescue, and gets in way, way, way over her head.

Harry/Tom/Ginny
"Rape the Willing by Proserpina R -- You can't.

"The Very Thought of You" by Abaddon -- Three dark, angsty Tom/Ginny/Harry drabbles, the first and second one related.

Other
Harry/Lucius/Tom: "Beyond This Point Lie Monsters" by Hijja R -- When Harry sneaks into Hogwarts nether regions to spy on a visiting Lucius Malfoy, he has no idea what he's getting himself into.

Harry/Hermione/Snape: "Waiting For Hell" by Liz Barr NC-17 -- Dumbledore dies and Ron disappears, and now they're just waiting for Hell to open up.

Oliver/Marcus/Terence: "About The Z-Axis" by Drew NC-17 -- Oliver lurks and watches. And then, he does a hell of a lot more than just watch.

Remus/Hermione/Snape: "The Darkest Evening of the Year" by kphoebe R -- Hermione Granger kisses Remus Lupin in the garden of Number 12 Grimmauld Place that Solstice evening, there are snowflakes caught in her eyelashes.

Harry/Draco/Luna/Ginny: "The Absinthe Drinkers" by foreword NC-17 -- Much to Draco's dismay, he is discovered by Harry, Luna and Ginny in the Hog's Head. Even worse; they force their company upon them. Things improve.