Nelson's Compact Bible Dictionary is an accurate and thorough A-to-Z resource. Complete with teaching outlines to make lesson and sermon preparation easier.
This book is always right next to my Bible. I read it just after I read a section of scripture and it gives me extra bits of history, facts, and insight about the text that I may not have known or figured out. It doesn't do EVERY verse but it hits all of the major topics found in scripture. I'm sure there are better commentaries out there, but this one is very good for someone just looking to get a little extra out of reading their Bible.