http://www.book-editing.com/
A network of professional editors and writers providing manuscript editing and proofreading.  Nothing compares to the unbiased eye of an expert.

http://www.amazon.com/Writing-Sell-Scott-Meredith/
Writing to Sell by Scott Meredith.  Each chapter cuts to the essentials of what every writer should know before penning a work of fiction.

http://www.sfwa.org/
Science Fiction and Fantasy Writers of America (SFWA).

http://thesaurus.com/
As my mother-in-law once said, 'Any writer worth her salt uses a thesaurus.'

http://www.writingforums.org/
Get critiqued and see the work of other aspiring authors.

 

http://www.nelsonagency.com/  
Tips on query letters and an insightful blog on the publishing industry.