Just to bring more (confusion) to the discussion, "effect" can actually be a verb as well...
See following examples, with the verbs used in the past tense:
Affected" means "impacted, created an effect on, changed in a certain way."
Example: The BP oil spill adversely affected marine wildlife in the Gulf of Mexico and surrounding areas.
Effected means "executed, brought about, produced something."
Example: After the BP oil spill, the government effected (brought about, executed) sweeping environmental regulation.