Bill Jelen 
Excel Gurus Gone Wild [PDF ebook] 

Drawn from actual excel conundrums posted on the author’s website, www.mrexcel.com, this high-level resource is designed for people who want to stretch Excel to its limits. Tips for solving 100 incredibly difficult problems are covered in depth and include extracting the first letter of each word in a paragraph, validating URL’s, generating random numbers without repeating, and hiding rows if cells are empty. The answers to these and other questions have produced results that have even surprised the Excel development team.