Best books for an introduction to statistical data analysis? I bought this book:
How to Measure Anything: Finding the Value of Intangibles in Business 
and 
Head First Data Analysis: A Learner's Guide to Big Numbers, Statistics, and Good Decisions
What other books would you recommend?
 A: This book is dynamite:
George E. P. Box, Statistics for Experimenters: An Introduction to Design, Data Analysis, and Model Building
It starts from zero knowledge of Statistics but it doesn't insult the reader's intelligence. It's incredibly practical but with no loss of rigour; in fact, it underscores the danger of ignoring underlying assumptions (which are often false in real life) of common tests.
It's out of print but it's very easy to find a copy. Follow the link for a few options.
A: I didn't find How To Measure Anything, nor Head First, particularly good.
Statistics In Plain English (Urdan) is a good starter book.
Once you finish that, Multivariate Data Analysis (Joseph Hair et al.) is fantastic.
Good luck!
A: I am a big fan of Statistical Models - Theory and Practice by David Friedman. It  succeeds remarkably well to introduce and motivate the different concepts of statistical modeling through concrete, and historically important problems (cholera in London, Yule on the causes of poverty, Political repression in the McCarty era..). 
Friedman illustrates the principles of modeling, and the pitfalls. In some sense, the discussion shows how to think about the critical issues and is honest about the connection between the statistical models and the real world phenomena.
A: The classic "orange horror" remains an excellent introduction: Exploratory Data Analysis by John Tukey. 
http://www.amazon.com/Exploratory-Data-Analysis-John-Tukey/dp/0201076160
A: My favourite book on Statistics is is David William's Weighing the Odds. Davison's Statistical Models is good too.
A: Statistics as Principled Argument by Abelson is a good side book to learning statistics, particularly if your substantive field is in the social sciences.  It won't teach you how to do analysis, but it will teach you about statistical thinking.
I reviewed this book here
A: The best intro in my eyes is the following one:

David Howell - Statistical Methods for
  Psychology

It is the BEST in making statistical concepts understandable for non mathematicians so that they get the math afterwards!
Unfortunately it is updated every year and, hence, pricey.
A: You might find useful this one: The Elements of Statistical Learning: Data Mining, Inference, and Prediction
UPDATE #1:
This book might be useful as well: O'Reilly: Statistics in a Nutshell
A: *

*Wilcox, Rand R. - BASIC STATISTICS - Understanding
Conventional Methods and Modern
Insights, Oxford University Press,
2009

*Hoff, Peter D. - A First Course in
Bayesian Statistical Methods,
Springer, 2009

*Dalgaard, Peter - Introductory
Statistics with R, Second Edition, Springer, 2008
also take a glance at this link, though it's R-specific, there are plenty of books that can guide you through basic statistical techniques.
A: As a biologist, I found the Sokal and Rohlf text to be quite readable, despite its voluminous-ness. It's not so great as a quick reference, but does walk one through statistical theory.
R. R. Sokal and F. J. Rohlf, Biometry the principles and practice of statistics in biological research, Third. (New York: W.J. Freeman and Company, 1995).
A: An old favourite of mine as an introduction to biostatistics is Armitage & Berry's (& now Matthew's):
Statistical Methods in Medical Research 
A: Agresti & Finlay's Statistical Methods for the Social Sciences is quite good, though I'd like to believe there is a good open source alternative.  Is it wrong to use an amazon affiliate link here?
