I recently attended a Hadoop Users Group meetup. Here are some of the suggested material to learn more on Hadoop and it's ecosystem.
Essentials for Appache's Hadoop - Register and watch six recorded webnairs from Cloudera on Hadoop.
Yahoo! Hadoop Tutorial - A series of tutorials on how to how to use the Hadoop distributed data processing environment
Hadoop: The Definitive Guide - The Hadoop Bible
O’Reilly Ecosystem books - Hive, Pig, Hbase, Cassandra, others
Hadoop in Action and Hadoop In Practice - Example-based books. Very pragmatic, get you up-to-speed quickly
Other Links :
Cloudera Training & Distributions
http://www.cloudera.com/resources/
https://ccp.cloudera.com/display/SUPPORT/Downloads
HortonWorks Training & Distributions
http://hortonworks.com/community/
http://hortonworks.com/download/
Hadoop World 2010, 2011, 2012 - Slides and video
http://www.hadoopworld.com/
Cloudera Essentials Series – 1 to 6 (Audio) http://www.cloudera.com/search/?q=essentials
Apache Hadoop – Petabytes and Terawatts
http://www.youtube.com/watch?v=SS27F-hYWfU
History of Hadoop
http://www.wired.com/wiredenterprise/2011/10/how-yahoo-spawned-hadoop/
Adam Bosworth Interview from 2005 (source of some quotes in this presentation)
http://itc.conversationsnetwork.org/shows/detail571.html
An Intro to Hadoop – Mark Fei
http://cdn.oreillystatic.com/en/assets/1/event/85/An%20Introduction%20to%20Hadoop%20Presentation.pdf
YARN/MRv2 Information (Next-Generation Hadoop)
http://blog.cloudera.com/blog/2012/02/mapreduce-2-0-in-hadoop-0-23/
http://hadoop.apache.org/docs/r0.23.0/index.html
Brad Hedlund - Understanding Hadoop Clusters and the Network
http://bradhedlund.com/2011/09/10/understanding-hadoop-clusters-and-the-network/#download
