This is a very modest list for now. More is coming.
HANDY THINGS
Scarf-O-Matic
Thanks to Kristopher Miller for maintaining this handy tool
YARN SOURCES
Knit Picks
excellent value-priced yarn
Universal Yarn
some of the best colors
Yarn Country
good online store for Plymouth Galway
Jimmy Beans Wool
good online store for Cascade 220 and Cascade 220 Superwash
Casco Bay Cotton Chenille
the only known source for chenille for the S18
IMAGE SOURCES
Tragical History Tour
many photos and video stills of the scarves in the Pyramids of Mars section
COSTUMING
Doctor Who Cosplay and Costuming
redirects to a highly active LiveJournal community
Tardis Dress
A resource for Tardis-based fashions, decor and jewelry
Prydon Academy
Doctor Who Costuming at Dragon*Con and Beyond!
Stitches in Time
Facebook group for scarf makers, wearers, cosplayers, prop makers, etc.