Try buying the 'Ultra Rare Trax' or 'Unsurpassed Masters' CD's. They're outtakes of the very first takes off the original studio recordings. It gives you amazing insights into how they composed their songs and how the eventual releases differed from the originals due to George Martins influence... ie, speeding up the recording slightly and adding orchestral arrangements. It's awesome listening to the original intrumental takes of Help or the first version of Strawberry Hill etc.
then seeing how the songs developed over time