I highly rec Days in Our Lives (http://community.livejournal.com/directors_seat/) by splashpink and titheniel Very long, amazingly hot stuff and with heaps of angst. It's a pornstar fic.

Easy to Say (Harder to Feel) (http://community.livejournal.com/thesacredmuse/?skip=80&tag=easy+to+say+verse) by ze_pink_lady and cherryscott Very long fic with heaps of angst. Its a hooker!jensen fic.

But Then My Homework Was Never Quite Like This (http://thenyxie.livejournal.com/481145.html) by thenyxie Not underage, but Jared is 18 and Jensen 26. Teacher!jensen and really hot stuff. But if you have a problem with d/s for whatever reason, be warned.

Dirt On Our Uniforms (http://beckaandzac.livejournal.com/315948.html) by beckaandzac Pretty long and has long sequel to boot. Both Js are underage, it's a highschool!fic

The Third Third (http://insane-songbird.livejournal.com/12682.html) by insane_songbird A college!fic that starts with the boys hating eachother. This one is R and all the others above are NC17.