Waiting on a second date
You had an amazing time on your first date. You laughed, talked and stayed out until the wee hours of the morning. He said that he'd call. Now three or four days have gone by, and you're still waiting for the phone to ring.
Should you call?
If he said that he'd call you, then the ball is in his court. Many men have "rules" for themselves on how long they should wait to call you. They don't want to seem desperate and scare you off. Maybe his rule is three days. Maybe it's a week. Or honestly, maybe he's not interested.
The only way to know for sure is if you have contact with him again -- so call him. If you don't feel ready to pick up the phone to talk, you can find other ways to get in touch. (See some ideas below.)
A friend of a friend
Did a friend set you up on the date? Do you know anyone who works with him? Ask around and see if they can find out what he's thinking. Maybe he's just been too busy to call, or maybe there's some miscommunication and he's waiting on a call from you. Dig around and see what you can find out.
Technology may help
If you don't want to actually call him, you can still reach out to him. Are you friends on Facebook? You can leave him a friendly message on his Wall without having to address the issue of another date. One message to his personal email account is another perfectly acceptable method of contact. (Note: Resist the urge to send more than one message "just in case" the first one "got lost" somehow.) Also, if you aren't comfortable calling, but have no problem texting him -- go for it. A text message could be the push that he needs.
Let it go
Did you think he could be Mr. Right? If not, don't worry about whether he's going to call or not -- let it go. Maybe he was just not that into you and that's okay. Move on to the next date. As cliche as it is, it's true: there are plenty more fish in the sea.