Most American children grow up learning the same ABC song (which incidentally has the same tune as Twinkle Twinkle Little Star). I don't know what is considered the most popular Korean alphabet song (가나다송), but there are a few on you-tube, some which are more simple, some more complex and some with a catchy tune and others that I can't seem to follow.
One of the more complex and fun Korean alphabet songs is this one to the tune of Doe a Deer (from Sound of Music....I love this musical!):
This cute song is featured on an iphone app called Ding Dong Deng - Han-Geul (딩동댕 한글-동물편).
There are free and paid versions of both the iphone app and the ipad app. The free version allows all the games, matching, writing exercises, etc for only ㄱ ㄴ ㄷ.
Here's the lyrics in hangul to the cute alphabet song where each letter represents a different animal (there are 14 consonants in the Korean alphabet and their are 7 notes in do re mi fa so la ti, so it's a perfect fit!)