Here are a few links relating to Physics2D.Net.

Erin Catto's Site (The mastermind behind Sequential Impulses.)     Game Physics

A 2D Physics Engine for XNA:                                                  Farseer Physics Engine

A OO C# Wrapper for SDL (The Library I use for the Demo)     SDL.Net

A collection of C# Wrappers of portable Game Libraries.              Tao Framework

My Original 2D Physics Engine:                                              Physics 2D

A Game Engine that uses Physics2D.Net                                 Xilon Engine II.Net