Phaser Effects

This effect is best not to describe, just listen to samples if you want to know what it does. If you really want to read Wikipedia has a nice article about phasers.

Causality 4 - As phasers go quite simple design.
Phase Evolution - A modded Phase 45 build that got additional phase stages for added phase'iness.
Phozer - A faux-phaser.

Sites with multiple circuits

Tonepad - Has four phaser circuits; MXR Phase 45, MXR Phase 90, Ross Phaser, Small Stone Phaser.