man sitting and reading a bookI have just started selling EBooks on Amazon. My first one is on Lookup Functions and is called A Comprehensive Look at Vlookup and Other Excel Lookup Functions.
Click here to check it out. 
This book provides a comprehensive look at the Lookup and Reference category in Excel. It starts by covering the LOOKUP function and then goes into great detail on the VLOOKUP function. You will learn how to use VLOOKUP, how to use it with Wildcards, how to use VLOOKUP to search through multiple sheets for a match and how to use VLOOKUP when a match is not in the first column of your table.
The course then takes a look at HLOOKUP. It continues and explains the advantages and disadvantages of INDEX MATCH versus VLOOKUP. The course then takes a look at the OFFSET function which allows you to set up calculations that automatically update as data is added. The INDIRECT function is also discussed and how to find data on other sheets in your file. A couple of minor functions such as HYPERLINK and TRANSPOSE are also briefly discussed.