garrison sheith
http://archiveofourown.org/works/11673693/chapters/26271711 (42k words. this is on my list to read. i heard nothing but good things about this monster)
http://archiveofourown.org/works/11974971/chapters/27083127 (82k words.)

Angst
http://archiveofourown.org/works/9077029 (6k words. mermaid shiro)
http://archiveofourown.org/works/10719255 (10k words, destructive keith with a shiro who secretly loves him)
http://archiveofourown.org/works/11152767 (9k words. SpacemalldressedKeith meets paladinshiro)
http://archiveofourown.org/works/9051163 (12k words.  one of best sheith stories that i've read. shiro goes back to a town he's left)

AU's
http://archiveofourown.org/works/11673693/chapters/26271711 (58k. treasure planet AU. Shiro's a cook, and Keith wants to fly)

http://archiveofourown.org/users/TruebornAlpha/pseuds/TruebornAlpha/works?fandom_id=10104017 (anything by these authors, I recommend Bitedown and Frostbite for Angst, and The Legend of the Sun and Moon for an epic tale)