Technology: Skyboxes, Skydomes, and Skyplanes

Skybox - A full cube mapped around the world geometry.
Pros: Full mapping; bottom of cube need not be hidden
Cons: Less realistic then alternate methods
Best For: General usage, Generic application

Skydome - A cube with no bottom (Is sometimes a half-sphere). Spherical texture mapping.
Pros: Most realistic
Cons: Most GPU-intensive, bottom of cube needs to be hidden, e.g. with terrain
Best For: Non-cosmos scenes, High realism applications

Skyplane - A flat plane placed above world geometry (Can sometimes be curved).
Pros: Best for some fog implementations, least GPU-intensive
Cons: All but top must be hidden
Best For: Valleys, Castles, Mountains, etc.