If you have every considered collecting colonial paper money you need to have at least one copy (I have 7) of The Early Paper Money of America by Eric P. Newman.  It is the best reference available today on the topic of collecting colonial paper money.  The good news is that the book is available for free!  You can access a .pdf version of the book here: https://archive.org/details/earlypapermoneyo2008eric

Now go out and start collecting!