Useful Links
PROJECT GUTENBERG is an effort to make every written work not under copyright available to everyone with an Internet connection. Thousands of full-length and short works (novels, short stories, poetry) can be found here.
FULL BOOKS is another site where you can read or download complete works for free, many of them in fields other than literature, such as the social sciences, math and science.

LIBRIVOX is the site for you if you like to listen to books.  Volunteers have created MP3 files of thousands of non-copyright works which are available for free download.  Since most are not pros, the quality of the reading can be variable.  Most of what I've listened to is quite good.  And if you like to read aloud to others yourself, you can volunteer to make recordings to be posted at Librivox for other users.
AUDIOBOOK CORNER has some amazing free audiobook downloads of books you actually want to listen to.  Enough said.

POETS.ORG  is by the Academy of American Poets and has an extraordinary archive, with an emphasis on living poets, and frequently containing sound recordings of the poets reading their own works.  A definitive site.
POETRY OUT LOUD is a marvelous site that was brought to my attention by a student.  Not only does it have a superb selection, but you can hear a lot of the poems read.  There are also video highlights of recent winners of the National Recitation Contest. 
POETRY 180 is a project by the Library of Congress to provide a modern poem for every day of the school year.  Hosted by former US Poet Laureate Billy Collins, you should find something in this site which is challenging, funny and COMPLETELY UNDERSTANDABLE.

FAVORITE POEM is another great project in which all types of Americans, old and young, rich and poor, famous and not are asked to read and discuss a particular poem which has special meaning to them.  I like this site because none of the poems have been posted because they might be "good for you" or they are "famous and important" poems.  These are poems (and many of them are famous) that actual, real, walking-around-trying-to-get-through-the-day people LOVE.

POETRY SLAM is the home of the art of competitive performance poetry.  If you've ever seen Russell Simmons' Def Poetry Jam, you have an idea what it's like; except that a real slam has judges selected at random from the audience and they are TOUGH.  This movement is proof positive that poetry is not for the faint of heart (or the dead).  You can see a pretty good video about the National Poetry Slam here.  Caution-- some of the language used in some of the poetry may be objectionable to some people.

THE MOTH is a site about storytelling in front of live audiences by professional and amateur writers.  You may not want write the Great American Novel, and you might not be the poetic type, but nearly everyone knows some stories to tell.  Check out the podcast on this site, too.  (Also available through iTunes.)  Caution-- some of the language used by some of the storytellers may be objectionable to some.
THE ELEMENTS OF STYLE by William Strunk is a little list of 18 rules and 3-4 general notes which comprise just about everything you need to know about writing.  There are very good updated versions of this book, especially those edited by the estimable E.B. White, but the precepts of the original have never been bettered.  Besides, it's hard enough to master these.  Remember Rule 13:  OMIT NEEDLESS WORDS!

THE WRITER'S ALMANAC is a daily podcast about writers and writing by Garrison Keillor, novelist and broadcaster, probably most famous for the film A PRAIRIE HOME COMPANION, which was inspired by Keillor's radio show.  It's a quiet an elegant five minutes, and if you can't download the podcast, you can read the text each day on the website.  (Also found at the iTunes store.)

GRAMMAR GIRL:  QUICK & DIRTY TIPS FOR BETTER WRITING is a podcast with a fairly self-explanatory title, although matters of style and usage are also addressed, all with good humor and wit by the creator, Mignon Fogarty.  Again, the shows are under ten minutes long, and you can read a transcript on the site.  (And you can find it at the iTunes store.)

AUTHORS ON TOUR LIVE! features podcasts by authors who are currently making the book tour circuit.  Authors to be found in the archives include David Sedaris, Joyce Carol Oates, Jane Smiley and Barack Obama.  (Also--surprise!--at iTunes.)
GRAMMAR BYTES has dozens of interactive games that help you correct common errors in grammar and usage, and most of the games will keep score for you and help you understand the correct answer.
GUIDE TO GRAMMAR AND WRITING has grammar quizzes, but a whole lot more.  Excellent tips and guides for writing--it would take weeks, perhaps months to work through all the valuable material found here. 
FREE RICE is a vocabulary-building site with something extra.  For every correct answer, 20 grains of rice are donated through the UN World Food Program to end world hunger.  It costs you nothing but a little time, and you can help feed a hungry child.
FLASH FICTION ONLINE is a great place to read and read about extremely short short stories (under 1,000 words).  This form has been around awhile, but with the advent of online reading, the demand for a story that fits on a single screen has increased.  Check it out--it's a great way to get your feet wet in the world of fiction writing.