Large size currency continues to be a driving force in the hobby.  People are attracted to the designs on the reverse, some consider it artwork.  Its resale value is enormous.  The only problem is the cost of these notes are skyrocketing.  Thats good if you already own some but bad if you are just starting.  If you are trying to break in, you might think about series 1914 Federal Reserve notes, 1923 silver certificates, 1917 United States notes, even 1922 gold certificates.  These examples can get pricey as well, but you can find some lower quality notes at a decent price.Don't be discouraged about the higher prices.  Just remember, you get what you pay for.  These are old notes and the prices won't be going down.