These are some of the links I have found useful and/or interesting as both a writer and a reader.

General:

http://www.writeon.ipfox.com

www.writernet.co.uk

www.litscene.com

www.author-network.com

www.writing.com

www.wordup.co.uk

www.absolutewrite.com

www.writers-editors.com

www.bloomsbury.com

www.artslynx.com

www.winningwriters.com

www.creative-writing-secrets.com

www.creative-writing-secrets.com

www.firstwriter.com

www.writers-editors.com

www.burryman.com

www.bbc.co.uk/writersroom

www.writersdigest.com/101sites

Plays:

www.plays4theatre.com

www.stageplays.com

www.amdram.co.uk 

www.heniford.net/1234/index/htm

www.doolee.com

www.scriptcircle.co.uk

www.uktw.co.uk

www.amadrama.co.uk

www.scda.com

www.playsandsongs.com

http://groups.com/AbsolutelyTheatre

www.performingwrites.com

www.paaw.com

www.storyfoundry.com

www.playscripts.com

www.findaplay.com

www.ravenbeard.co.uk

Poetry:

www.poetrysociety.org.uk/

www.thepeoplespoet.com

www.poettext.com

www.poethunter.com

www.poetrykit.org

www.poetrymachine.com

www.poeticvoices.com

www.poetrypoetry.com

www.andromeda.rutgers.edu/~jlynch/Lit/

www.everypoet.net

www.pmpoetry.com

www.hangtide.com

www.poetry.net/topsitesw/rankem.cgi?id=Jamaub

www.warpoetry.co.uk

Travel writing:

http://main.travelwriters.com

Publications

www.writers-forum.com

www.writersnews.co.uk