There also are several short story initiatives that invite to participate, they are marked in red.
National Short Story Month - the history of short story month by Poets+Writers: "The concept has some history behind it. The Emerging Writers Network kicked off its first Short Story Month in 2007, and Larry Dark, director of The Story Prize, floated the idea even earlier." - Official links: Emerging Writers Network + The Story Prize Blog.
Short Stories in Daily s-Press: story collections (by Walter Bjorkman, Tania Hershman, Eric Beeny, Meg Pokrass and many others); anthologies (Writers Abroad, International Short Fiction, optimistic SF, ....); short story writing guides (Short Circuit); author talks
100 Story Links in Honor of Short Story Month 2011 - a list-in-progress by Flash Fiction Chronicles, writers are invited to share their flash story recommendations by posting on the flash fiction chronicle wall
The storySouth Million Writers Award - long list with 158 notable short stories of 2010, shortlist upcoming Friday, 20th May
#storysunday - a twitter initiative: on sundays, link to someone else's short story published somewhere online which will delight and astound readers this week. if you aren't on twitter, there's an online stream
52/250 A Year of Flash - a year-long writing initiative, now completed: 52 themes in 52 weeks, dozens of authors, hundreds of stories. (Daily s-Press feature)
The Short Story Reader - a blog about good stories on the web and other reading (Daily s-Press feature with interview)
Short Story Collection Giveaway Project - readers are invited to promote one of their favourite story collections by blogging about it and offering a copy as giveaway
The Short Review - online reviews of new, not-quite-so-new and classic collections and anthologies (Daily s-Press feature)
Short Story Month blog by Mat Bell - daily reviews of short stories published in print literary magazines