Charlie is one of the friendliest names on the planet, and Good-time Charlie is back. More and more parents (of babies of both genders) these days are opting to put the friendly, genial Charlie on birth certificates--though we'd recommend you use Charlie as a pet form of the more serious Charles. In the UK, Charlie is the fourth most popular name for boys.
Charlie has dozens and dozens of pop cultural references, from Charlie Chaplin to Charlie McCarthy to "Charlie's Angels" to Charlie Parker to Charlie Sheen to Charlie Rose. It derives, of course, from the classic name Charles which, in turn, comes from a German word meaning "free man." Charles became very popular in France during the Middle Ages due to the fame of Charles the Great, aka Charlemagne.
Putting nicknames on the birth certificate is very much a growing trend. Current celebs who have chosen Charlie for their sons include Tiger Woods, Mimi Rogers, Soledad O'Brien and Sarah Chalke.