GuerrillaCG Modeling Series
Guerrilla CG : Subdivision Topology Artifacts
Subdivision Topology: Artifacts from The Guerrilla CG Project on Vimeo.

From Guerrilla CG:

In this video Greg Petchkovski explains how a the *topology of a model can drastically affect the smoothing of a model. He demonstrates key concepts to avoid unwanted smoothing artifacts. A must watch for anyone wanting to model with sub division surfaces. (5:29)

*Topology is simply the wireframe pattern of a polygon mesh.
GuerrillaCG Modeling Series (Beginner)
GuerrillaCG : The Polygon
GuerrillaCG explains the polygon: the basic building block of all 3d models.
GuerrillaCG : Multisided Polygons
GuerrillaCG explains multisided and intersecting polygons.

GuerrillaCG : Objects
GuerrillaCG explains objects and why they are useful.
GuerrillaCG : Primitives
GuerrillaCG explains primitives, and how to use these convenient starting points.

GuerrillaCG : Subdivision Artifacts
GuerrillaCG explains the relationship between topology and smoothing.