DirectX 9
planar reflections in directx Planar Reflections (work in progress)

How to implement local planar reflections using render targets, and a comparison of this with other methods.
directX user clip planes

User Clip Planes (work in progress)

Shows how to setup clip planes. Clip planes in DirectX are trickier than their OpenGL equivalents.
OpenGL
opengl lens flares Lens Flares (work in progress)

Shows how to draw lens flares in screen space whose brightness depends on how much of the sun is visible.