(This is a far from comprehensive list and gets updated and added to when I remember.  I'm always happy to hear about any interesting sites/people/organisations - send them to info[at]peternagle.co.uk)

Music
My SoundCloud page

My Score Exchange page


Other things I do

Tales from the Back Desk

Big Dog's Kennel

Organisations and Events

Sound and Music

Kensington Symphony Orchestra

Music We'd Like To Hear
The Wulf

Wolf Pack

Just Intonation and other microtonal resources

 

Tonometric - test your ears to see how accurately you can hear small intervals.

Ben Johnston's notation system: article by Marc Sabat

Xenharmonic Wiki

Microtonal resources for instruments:

Flute
http://cnx.org/content/m14070/latest/

Oboe
http://www.21stcenturyoboe.com/index.php

Bassoon:
http://www.idrs.org/resources/bsnfing/finghome.htm

Bloggers
Boring Like a Drill
The Rambler

Composers and Musicians
John Luther Adams

Captain Beefheart

Laurence Crane
Angharad Davies
Rhodri Davies

Julius Eastman

The Fall

Michael Finnissy

Morton Feldman

Kyle Gann
Ben Harper
Ben Johnston

Mary Jane Leach
Alvin Lucier 
Microtonal Projects
Phill Niblock
Tim Parkinson
Harry Partch
Rarescale
Heather Roche

Galina Ustvolskaya

Daniel Wolf