Your first book:
Study Bible

Second book:
Bible Dictionary/
Encyclopedia

Third book:
Concordance

Fourth book:
Commentary

Fifth book:
Word Study

Sixth Book:
Atlas

The World Wide Study Bible is comprehensive.  
A third option many will see as the  best Online Study Bible option: Alexander Scourby reads, preachers preach from the pages of the ONLINE STUDY BIBLE.COM  Featured site info

 

The ISBE SearchGodsWord.org is easy to read and extenisve. The one at BibleMaster allows you to click to the next entry, just like reading a book.  This is a handy feature. 

BibleGateway.com is  easy. For full concordance functions such as Strong's numbers and original-language definitions use BlueLetter or Crosswalk (see the 5th book on this chart).  

At BlueLetterBible.org,
type in a verse or chapter, then click on "L" for Listing of the commentaries. 


The online concordance functions also help with word studies, but Blue Letter has Vines Dictionary for the New Testament. After finding your verse, click on "D" and scroll down to Vines.