Some websites I've found useful:
www.oxfordyoga.co.uk
All things Ashtanga, especially in Oxford. Oxford is lucky enough to have a thriving Ashtanga community and attracts top teachers from around the world
www.hathayogacenter.com
My teachers. Interested in training to become a yoga teacher? Try their retreat in beautiful Bali
www.freespirituk.com
Fantastic yoga holidays with amazing yoga teachers, all over the world
www.ashtanga.com
All things Ashtanga, including a Moon Days calendar and workshops by officially certified teachers
www.yogamatters.com
For all your yoga purchases. My favourite is Matthew Sweeney's Chandra Moon Sequence poster (in the Ashtanga Posters section)
www.kpjayi.org
Shri K Pattabhi Jois - the official head of the Ashtanga Yoga school