The (Submission) Grinder is a free online submission tracker and literary market database for fiction writers. Users can search for new markets for their stories, limiting their results by genre, preferred word count, payment, and average response time (the search feature works best in Google Chrome). The database is very strong on markets for speculative fiction, and constantly updates for when markets are temporarily or permanently closed.
With a free account, users can record their submissions, create lists of markets to follow (ie, markets to submit to), and view aggregated submission data from the Grinder community--it can really help alleviate the post-submission jitters to know just how long a market takes to get back to prospective writers!
Science Fiction author William Shunn has the definitive guide to proper manuscript format for short stories on his website. Click the link above to read his guide or download it as a PDF.