Chandoo runs a great Excel site at chandoo.org. I really like his site because he frames Excel problems from the viewpoint of a real life data analyst. He’s been one and he knows what makes analysts great.
Here’s a great quote on what to emphasize in your spreadsheet modelling — usefulness to clients, not obscure, needless formulas.
This is not to say it’s unimportant to have a deep Excel toolbox….this can greatly improve efficiently and depth of analysis. However, it’s just a tool, not the goal in itself.
Quote from “The VLOOKUP Book – Definitive guide to Microsoft Excel lookup formulas” by Purnachandra Rao Duggirala –
“I see many analysts wasting hours of time trying to fine tune their formulas. The reality is your bosses or clients never ask for fastest spreadsheets. They ask for most usable, accurate and simple ones. So instead of focusing your energies to reduce the length of your formulas or trying to use complex ones, you should spend time impressing your bosses & clients.”
Start reading this book for free: http://amzn.to/1XEvY1j