Do I have to pick just three?
I think my all time favorite is Let's Pretend the War is Over, a Harry/Draco fic by pir8fancier. As a matter of fact, pretty much anything written by her is great. Lettered is my second favorite of her stories (also H/D).
VeresnaUssep's OFC in Love's Labours; Paradise Lost manages not to be a Mary Sue, and the story is captivating.
Tarie has an interesting fixation with Tea in my two favorites of her stories, Tea Service, a Harry/Hermione/Draco fic, and Tea and Being Free a Ron/Draco fic.
And anything by Ms_Figg although I think The Ring is my favorite so far.
As far as fellow Forumites, I love dazzledfirestar's Mary-Sue Virus (how couldn't I? I'm in it!!) and her X-Men Romy fic Curious. Pretty much anything written by polywolly (who writes beautiful SS/HG fics), but When You Least Expect and Shall I Forget are my favorites. Cailyn -Pixagi- Webster's Harry/Draco story Sheep in Wolf's Clothing and its sequel I Control You, are both amazing. I enjoyed What Did You See? a Sevmione PWP by Madapple, and I am looking forward to her Mundungus/Umbridge fic with much anticipation. lol! I am slowly working my way through StoryJunkie's Fics; Office Mess was hot, O Brother was disturbing, but hot, and her Monster Porn is definitely promising. NightScribe did an awesome job on The Gryffindor and the Grease Monkey, and I am planning on digging into Iniquitous Desires next as all her talk about it has me intrigued. Redsliver's From the Looking Glass, even though I've only read the first three chapters - I swear I'm going to finish it one of these days! Keith's Mad Scientist Porn series. And last, but certainly not least, Trae's contest story, Special Delivery.
If I didn't mention you it's only because I haven't gotten around to reading anything you've written yet. I'm not trying to play favorites, really!