Well, normally just "Hello" but when it's a friend or someone I speak to often, I could answer in a variety of different ways.
But there was this one time when my caller ID stopped working because we had just moved, and my friend was over and another one of my friends told me he was going to call, so I answered the phone with an extremely high-pitched scream and it turned out to be someone doing a survey. After they didn't say anything for about ten seconds I said "Dusty!" and the girl went "excuse me?"

then I went holy S___! and hung up.

Dusty called about two minutes later.... I answered by screaming.