Critters Writers' Workshop
Critters is an on-line workshop/critique group for serious writers of Science Fiction, Fantasy, and Horror. You get your work critiqued in exchange for critiquing the work of others, both of which are invaluable ways to improve your writing. It's run by Dr. Andrew Burt, currently vice-president of SFWA, and his army of software minions.
SFF Online Writing Workshop
Online Writing Workshp for Science Fiction, Fantasy and Horror
"OWW SF&H is an online community of writers of science fiction, fantasy, and horror--brand-new and published--who help each other improve their work. Whatever your level, the workshop can help you grow as a writer--through the useful critiques you receive and through what you learn by reviewing the work of others."
"Writing.Com is the premiere online community for readers and writers of all ages and interests. Whether you are a casual reader searching for a good story or an enthusiastic writer looking for the perfect place to store and display your masterpieces, Writing.Com is the website for you!"