Early on, I wrote a post about my MXR Phase 100, but I stumbled across a great deal at Amazon for the MXR Phase 90. Both the MXR Phase 90 and Phase 100 are great pedals with a nice classic phase effect. The Phase 90 is a really simple pedal with a single knob to control the speed of the phase (phase 100 can control the wave pattern as well as the speed).
Currently, the MXR Phase 90 lists for $150, but is currently on sale at Amazon for a killer price of $66.27 (which includes FREE super saver shipping). While doing some research I came across a great video showing a shoot out between the MXR M-101 Phase 90 vs. MXR CSP-101CL Custom Ship Script Phase 90.