Here's a sample of some of my favorites. Not nearly ALL of my favorites, because there are far too many to rec. Some of the recs below are not strictly J2 or Sam/Dean fics; please give them a try, even if they're not your regular pairings - you will be pleasantly surprised, I assure you!
Cemetery Dreams - Jared/Jensen, NC-17 - beautifully written supernatural/HS AU fic
I will follow you into the dark - Sam/Dean, R - later-life Winchesters. Mind the warnings, and know that this fic made me ugly cry but it was gorgeous and perfect.
Southern Hospitality - Jared/Jensen/Danneel - NC-17 - my favorite OT3, in a brain-meltingly hot fic.
Black Irises and Sunshine - Jared/Jensen - R - HS AU fic, memorable characters with a wonderfully misfit Jared that I would love to see so much more of.
Set Out Running Sam/Jensen, R - such a unique pairing, in a gorgeously angsty Sam POV set in s8.
Be My Angel? Jared/Jensen, NC-17, supernatural/HS AU - loved the tone of this and the unique approach taken
Nothing Can Come Between Us Sam/Dean/OFC, Sam/Dean, NC-17 - a perfectly-done, boys finally giving into their need for each other fic.
The First of Many - FANART - Sam/Dean, PG - stunningly gorgeous piece with bonus!facial hair and tattoos
Souls Are Overrated - FANART - Soulless!Sam/Dean, NC-17 - beautifully done art with bonus nudity and restrained violence. And did I mention Soulless!Sam??
Letters from a Half-Finished Boy - Sam/Dean, R - absolutely breathtaking fic, with a beautiful, lyrical writing style
I'm Sorry Sam/Kevin, PG-13 - wonderful, angsty s9 fic.
Stay With Me A While Jared/Jeff, NC-17 - hot and lovely fic with one of my favorite, sadly-too-rare pairs
Early Morning Yesterday- Jensen/Jeff, R - sexy, happy-making fic with a pairing that needs to happen more!
Moments - Jensen/Jeff, PG-13 - sweet, fun fic because we need more JDM in all the things.
Second Thoughts - Genevieve/Adrienne, PG - sweet, angsty fic, wonderfully written with a cool premise.
OK, I wanted to keep it to ten but went way over, but I'm sure you'll forgive me for my excesses, right? Right??