Tracking comments so hard. XD

I read another split personality fic by kellifer_fic just before this request, so I'm looking forward to the other. Thanks for these!

The Crowded Room (http://kellifer-fic.livejournal.com/270965.html") - the psychic kids are Sam's split personalities.

There's Underneath the Weight of it all by Moirnthewicked here:
http://users.livejournal.com/_mournthewicked/220635.html
It's a J2 AU and Jared has multiple personalities and one of them is Sam except he's not really like Show Sam so it might not be what you're looking for but it's still really really good so you should read it anyway (if you haven't already!) And there's a sequal too that is also awesome.

I second this rec HARD! I love that universe and the way the author dealt with the different personalities was wonderful!

I actually stumbled across this just after making this post and blew through both stories. Not quite the Sam I was looking for, no, but still excellent! Thanks!

This is a series of I think 3 or 4 character bleed stories. The links to the sequels will be on the page somewhere.
"Method Acting" http://parenthetical.livejournal.com/68775.html

A oneshot, J2(Sam/Dean):
"Character Bleed" http://lazy-daze.livejournal.com/629871.html

This isn't exactly what you're looking for. But Jensen does have alternate personalities (of the characters he played in tv/movies). It's a Dollhouse AU if you've ever seen that tv show(I haven't but loved the story):
"Stained Glass Masquerade" http://splashpink.livejournal.com/199514.html

Jensen has MPD, but not of his tv/movie characters:
"The United States of Jensen" http://takobella.livejournal.com/4826.html

Thank you tons!

It'd probably interesting if the personalities were characters from other things the actor has done, i.e. Dean switched into Priestly or Jason Teague etc...

"Stained Glass Masquerade" does this