submission grinder – A database of markets for writers. Subscription is free.
duotrope.com – Similar to Submission Grinder but is a paid service.
critters – for serious writers of science fiction, fantasy and horror
Creative Challenges for Writers
National Novel Writing Month (NanoWrimo) – The challenge is to write a 50,000 word novel in 30 days. Happens every year in November.
StoryADay – Write a short story every day for a month. Happens every May and sometimes in September.
National Poem Writing Month (NapoWrimo) – Write a poem every day for a month. Held in April every year.