I have just read the newest post of DOGHOUSEDIARIES, and I am wondering whether the words for characters are fixed in the USA or the UK, as I am not a native English speaker.
A as in apple
The closest thing might be the NATO Phonetic Alphabet.
Alpha Bravo Charlie Delta Echo Foxtrot Golf Hotel India Juliet Kilo Lima Mike November Oscar Papa Quebec Romeo Sierra Tango Uniform Victor Whiskey Xray Yankee Zulu
If you mean the names as we learn them in school, then they're very rarely written down (so I'm effectively inventing these spellings), but they would (in British English) be:
I get what you mean by asking about a is for apple; whilst I'm sure I was taught something like that when first learning to read, it has been so infrequently used since then (I'm now 35) that I honestly couldn't tell you what they were. The letter names above, though, are how I would spell out my name to someone unfamiliar with it, for example.
The Nato Phonetic Alphabet (Alpha, Bravo, Charlie, Delta and so on) would be familiar to some, but not to all — my mother would probably think me pretentious for using it. But that is what our police would use to provide clear, unambiguous details of a car number plate over the radio, for example.
I think a conventional alphabet that starts with "A is in Apple" is the one form esl.about.com. The purpose is to illustrate a prototypical word starting with each letter for pedagogical purposes (not necessarily to make the pronunciation of the letters distinct like a phonetic alphabet). That list says:
Bill posted a link to the law enforcement phonetic alphabet, namely. Here the idea is to make each letters word have a distinct sound.
The authors of children's books make a living constructing and publishing lists of interesting words for characters. For example, Sesame Street ABC Flash Cards
There are others on Amazon — search for Dr Seuss' ABC, An amazing alphabet book! and Thomas' ABC book. These books, and many more like them help children connect writing to the sound of nouns, a cornerstone of learning any language.