Emoji symbols were added to Unicode in its version 6.0 of October 2010, and Apple incorporated font support in iOS and OS X 10.7 shortly thereafter. An earlier article provides a link to a good list of them. When using these characters, it's helpful to be aware that :
A) Apple's Color Emoji Font embodies new technology and will not work in all apps. In particular the OS X iWork apps, iBooks Author, and iWeb display nothing (although iOS iWork apps and iBooks work fine). Win OS before Win 7 can't see them, nor can older mobile devices which still use pre-Unicode emoji encodings. An alternative black/white font which may work where color does not (except for flags) is Symbola.
B) The 10 flags which appear at the end of Apple's "Places" emoji category are not individual characters and can't be found as such in any Unicode chart. These are a sort of "ligature" of two Unicode "Regional Indicator Symbols". More info on this mechanism can be found on P. 534 here and here.