Welie.com. A pattern library with over 125 patterns for Interaction Design. All patterns are illustrated with examples and links to literature and occasionally code.
User Interface Design Pattern Library. UI patterns for web designers. See examples and read rationale, solutions, and implementations for each pattern.
MVC - Model, View, Controller. Entenda mais sobre o padrão de projeto MVC e entenda o motivo de ele ser usada em centenas milhares de projetos no mundo.