Here are a few word usages that I got from John Potter. He's a word-whiz.
lead/led: As a noun, lead is a kind of metal. As a verb, lead means "to conduct." A guide will lead a tour of the ruins. Led is the past tense of the verb "to lead"; He led the company for twenty years.
loose/lose: Lose is a verb whose past tense is lost: Did you lose your elevator card, again? Loose is generally an adjective for "not tight"; I have a few loose screws.
maybe/may be: Maybe is an adverb: Maybe the negotiators will succeed this time. May and be are verbs: The rumor may be true.
Hope these little tips come in handy. :)