Here you can find a compilation of helpful writing-related resources. Please note that I may not have had any personal experiences with the writing groups, retreats, or other websites listed below, and please read my link disclaimers.  

The WoMentoring Project
The Writers Site

Online Writing Groups
Where the Writers Go to Write -
Scribophile - The Online Writing Community
Critique Circle Online Writing Workshop
Review Fuse
Writing groups link collection on The Writers Site

Writing Retreats
The Writers' Retreat (worldwide)
10 of the Best Writing Retreats - (worldwide)
Arvon (UK)
Retreat West (UK)
Urban Writers' Retreat (London, Devon, England)
The Writing Retreat (Cornwall, England)
Fictionfire by the Sea (Cornwall, England)
Fielding Programme (Cove Park, West Dunbartonshire, Scotland)
Anam Cara (Ireland)
The Grange (Isle of Wight)
La Muse (
Labastide Esparbairenque, France)
Chez Castillon (Dordogne, France)
Paris Writers Retreat (France)
Limnisa (Greece)