These are some books written by members of the meetup.

Testing R Code

Richard Cotton

R Packages: Organize, Test, Document, and Share Your Code

Hadley Wichkam

A Quantitative Tour of the Social Sciences

Andrew Gelman & Jeronimo Cortina

R Cookbook: Proven Recipes for Data Analysis, Statistics, and Graphics

JD Long

R for Everyone

Jared P. Lander

ggplot2: Elegant Graphics for Data Analysis (Use R!)

Hadley Wickham

A Computational Approach to Statistical Learning

Bryan Lewis and Michael Kane

Learning R: A Step-by-Step Function Guide to Data Analysis

Python for Data Analysis

Wes McKinney

Bad Data

Q. Ethan McCallum

Forecasting: principles and practice

Rob Hyndman

Parallel R

Doing Data Science

Cathy O'Neil and Rachel Schutt

Data Analysis with R - Second Edition: A comprehensive guide to manipulating, analyzing, and visualizing data in R

Tony Fischetti

Applied Predictive Modeling

Max Kuhn & Kjell Johnson

Data Science at the Command Line

Jeroen Janssens

R for Data Science: Import, Tidy, Transform, Visualize, and Model Data

Deep Learning with R

JJ Allaire

Analyzing the Analyzers

Harlan Harris, Sean Patrick Murphy & Marck Vaisman

Pandas for Everyone: Python Data Analysis

Daniel Y. Chen

Feature Engineering and Selection: A Practical Approach for Predictive Models

Max Kuhn

Learning R

Text Mining with R

Julia Silge & David Robinson

Introduction to Empirical Bayes: Examples from Baseball Statistics

David Robinson

Service-Oriented Design with Ruby and Rails

Paul Dix

Teaching Statistics: A Bag of Tricks

Andrew Gelman & Deborah Nolan

Machine Learning for Hackers

Drew Conway & John Myles White

Machine Learning for Email

Data Analysis Using Regression and Multilevel/Hierarchical Models

Andrew Gelman & Jennifer Hill

Red State, Blue State, Rich State, Poor State

Andrew Gelman

Getting Started with D3

Mike Dewar

Bayesian Data Analysis

Andrew Gelman, John B. Carlin, Hal S. Stern, David B. Dunson, Aki Vehtari & Donald B. Rubin

Advanced R: Second Edition

Bandit Algorithms for Website Optimization

John Myles White