URL Description
HTML
W3Schools Nice HTML Tutorial
CSS Floats How I learned Floats
Responsive Web Design Shay Howe
SQL
Data Modeling Data Modeling 101. Shows the major Notation syntaxes
Database Normalization Normalization Stuff
SQL Good basic SQL tutorial
Subqueries Rob Sheldon's easy guide
General Programming
Learnable Programming
OOPS
Abstraction and Detail
Orthogonality and the DRY Principle