1- Mr. Lipset's Encyclopedias.
2- A current, or near current Standard Catalog
3- IF you collect or are interested in T206's, Scot Reader's Inside T206.
4- IF you collect or are interested in Old Judge cards, get The Photographic Baseball Cards of Goodwin & Company 1886-1890
5- A 4th edition of Mr. Sugar's Bible, 3rd is ok if you can't find a 4th.
6- Egan's list
7- IF you chase ZeeNut cards, Horne's Zeenut list.
I'm in total agreement to what they said above about the Encyclopedia. Parts are a bit dated, there are some typos. But there's lots of great information. It is the starting point.
A link to Mr. Reader's excellent work...
http://www.oldcardboard.com/t/t206/I...al-edition.pdf