I totally rec Bubble of Happiness by miya_tenaka, it's short, but it will make you smile

http://miyawriting.livejournal.com/27676.html#cutid1

then a classic, in my opnion: In Four Dimensions by entanglednow

http://archiveofourown.org/works/150263

After The Storm by morganoconner

http://shadow-legacy.livejournal.com/46034.html

Four's Company by mistalagan

http://archiveofourown.org/works/284155

then, since you don't mind self recs :) I wrote two foursome fics, you can find them here:

http://romennim.livejournal.com/tag/dean%2Fsam%2Fcastiel%2Fgabriel