Lie vs. Lay vs. Lie
Probably the most annoying of the irregular verbs, so annoying that they get their very own page. The present tense of these verbs is not so bad.
Lie has two meanings: to lie down (i.e., recline) or to tell an untruth.
Lay, unlike lie, requires a direct object. You lay something down.
Where things get messy is when we start talking about the past and when we need to use past or present participles.
Rather than having to memorize, I've made a few cheat sheets (right click and save).