Dies Area
It starts with headaches, and it ends in a clusterfuck. So, business as usual, Apocalypse-wise.
http://alchemyalice.livejournal.com/5255.html

A Few Small Repairs
The apocalypse is over; all is well. Except that Sam's feeling a bit rudderless and missing Gabriel more than he thought he would, and that Dean and Castiel are keeping secrets, and, oh, yeah, that John Winchester decided to rise from the grave and no one really knows why.
http://liadan14.livejournal.com/37406.html

Like Glass (http://community.livejournal.com/libraryofsol/130758.html) by entangled_now. Actually she has 2 pages' of Sam/Gabriel stories, although this is the longest, and they're all good.

Here's another one by entangled_now:
Follow Me Down (http://community.livejournal.com/libraryofsol/126850.html) and it's sequel, Dead Space (http://community.livejournal.com/libraryofsol/127644.html), add up to about 8K words.
Warnings: Mate or die scenery, slight magical influence
Summary: "Are you actually worried about me? That's kind of funny and something I'll no doubt mock you for endlessly later."

If you're in the mood for some humour:
Your Bottle Is Empty (But Your Glass Has Been Filled) (http://archiveofourown.org/works/73779) by jjtaylor (http://archiveofourown.org/users/jjtaylor/pseuds/jjtaylor)
Pairing: Gabriel/Sam Winchester
Summary: "Becky wants me to tell you that she's read everything so far and that she...thinks the romance plot is very compelling."

The following are WIPs:
Blessed is his Child (http://community.livejournal.com/ameonna1_writes/7198.html) by ameonna1
Characters/Pairings: Dean/Castiel, Sam/Gabriel, Michael/Lucifer, Anna/Crowley, Bobby, OC’s
Warnings: Minor language, Baby fic, no m-preg
Spoilers: Up to 5x10
Summary: Gabriel's lesson might be over but Dean's and Castiel's is just beginning

Saving 'verse (http://community.livejournal.com/criminal_savior/tag/saving%20%27verse) by heavenvhellvus
Pairing, character, genre: Gabriel/Sam, Dean, Castiel, hurt/comfort
Warnings: Spoilers up to S5, torture, bloodplay.
Summary: Based on a prompt by kijikun. "Demon!Sam/Gabriel. In darkness there can be such light."

Fighting Dawn Master Post (http://community.livejournal.com/butterflywrites/3401.html) by butterflywrites
Pairing: Sam/Gabriel, minor Dean/Castiel
Summary: Sam's psychic powers have been dormant since Dean killed the Yellow-Eyed Demon and his other powers have been gone since he stopped drinking demon blood. They return, with a vengeance, leaving Dean and Castiel unable to help and Sam unable to hunt. With the Apocalypse on their doorstep, they’ll be forced to call on Gabriel, but there’s only so much even an archangel can do…even one whose feelings for the hunter in question are all too unclear.

This one is actually wildly AU and, I think, non-linear as well, but I enjoyed it enough to bookmark it.
Dream A Little Dream (http://mia6363.livejournal.com/20724.html) by mia6363
Pairings: Sam/Gabriel, Dean/Castiel
Summary: If his Father had never shown him the face... the face with the adorable dimples and caramel-brown hair, this never would have happened. If he hadn't been consumed with bubbly laughter and long, long legs, he never would have left. Gabriel gave up halfway through the 16th century. Castiel didn't even know he was supposed to be looking.