Erin Catto 2d physics tutorial
Erin Catto wrote the Box2D physics engine and made a fantastic presentation/tutorial on 2d physics.
Physics engines for dummies (Blog Post)
Paul Firth (A games industry veteran of ten years, worked on Little Big Planet and Heavenly Sword) wrote a blog tutorial on how to model the physics behind 'Pong'. Its a...
2D Game Physics 101 (Online Tute)
Great interactive tute that runs you through the basics behind 2D physics with code examples.