Patterns and design:

The Modern Quilt Guild (must log in as a member to view some content)

Quilt block inspiration and tutorials:

How to supersize a quilt block
Quilt block library

Color palettes:

Play Crafts Palette Builder – use your own photo to find correlating solids
Play Crafts Color Play  
Design Seeds 
Rethink color
In Color Order’s The Art of Choosing – several articles to help you pick fabric and build a palette

Quilt math:

A Quilter’s Table round up
Blossom Heart Quilts HST math
Big Batch HSTs - 18 at a time!
More fast HSTs - 16 at a time!
Fabric calculator

Adding a zipper to a pillow:

Sew Katie Did
Stitched in Color
Modern Handcraft

Online classes:

Academy of Quilting