I write a lot of shorter stories myself (tons of drabbles, and some stories under 500-700 words). But it took me a while to track down other authors' work (including copying off stories to check the wordcount), and one of the authors had moved off of LJ (I've relocated her stories). I went up from my target goal of <=500 words to <=700 words here, and I still don't have the variety of authors I'd like. If you know of other short-fic gems, please chime in below in the comments!
Short SPN Gen:
"Gas Stations and Mini-Marts" drabble (100 Words) by witchofthedogs. The last line packs such a punch here.
"Stars" drabble (183 words) by witchofthedogs. I really miss having Witchy write in this fandom.
Shiver (177 words) by gravi_girl123, a little pre-Series slice of bittersweetness.
Old Denim (100 Words) by radiophonic. Fantastic use of the "Photographs" drabble prompt here. Pre-Series.
I Find My Brother In There (700 words) by whipper. This is a series of seven 100-word drabbles on color prompts, and while the author thought this was a throwaway story, I really didn't. Each is individually moving, and collectively they leave you breathless.
Will The Circle Be Unbroken (387 Words) by Olivia (whose stories are all collected here. Olivia is primarily a micro-ficcer, one of my favorites from the early days of the SPN fandom.
Lost (100 Words) by Olivia. This drabble is for the prompt "Crossover", and what a wonderful, unique take on that word she chose.
Bleed Like Rain (700 words), post-"Born Under A Bad Sign" by plutogirl10. This author is another of my favorite micro-ficcers. Such an incredibly concise use of words to create a resounding mood.
Perchance To Dream (three 100-word drabbles) by maygra. You probably all know of Maygra's ability to spin a long, complex and satisfying story, but she is versatile enough to pull off drabbles with the same level of skill.
When Siblings e-Attack (700 Words) by eighth_horizon. About 25% of this very popular all-texting story is to identify POV, so really it's almost shorter. \o/ Funny, perfect, and unusual humor piece with a bite of pathos.
Short SPN Wincest:
New World Coming (700 Words) by Olivia. This is a stark AU, written around Season 2, and it's a compelling and different view of the boys. One of my favorites by this author.
The Razor In The Apple (125 Words) by Olivia. Even in these few words, you can sense how trapped Dean feels.
Like Water Over Stones (125 Words) by Oliva. Beautiful language throughout, in this glimpse of the futility of denial.
Genesis (100 Words) by Olivia. Gorgeous, poetic piece: Life starts out like that, Like spilled stars.
Untitled (313 Words) by whereupon. This is another author with a spare, quiet style— her words are so carefully chosen. Sam twists into awareness with thunder echoing in his bones.
Untitled (401 Words, rated R) by plutogirl10: "We can never have this, can we?"
Milestone (417 Words, rated R) by plutogirl10. Really nice vignette, and the schmoop is so stealthy you'll only notice how it makes you feel.
If you enjoy these stories, please remember to leave the authors some love!