I played a game with my 2 year old to teach her the alphabet.  The first day we started out with a is for apple.  I taught her using magnetic letters and we played hide and seek with the letter A.  I placed it among the other letters and had her find it.  She absolutely loved this game.  It has made such an impression on her that everywhere we go she is pointing out A for apple.  She even located the letter A on her car seat tag, which was very small print.  Although we have learned other letters, this one seems to have made the biggest impression on her.