The Bay Area Hadoop User Group meetup has over 5.2k members. Meetups like these are hugely popular and provide great resources, slides, etc.
Searching Google brings back 820+ results for PDFs related to Hadoop from Meetup files. Lots of great information here.
Google inurl:files.meetup.com Hadoop for Hadoop resources or any other meetup topics you might find interesting. Over 76,000 resources by searching for just inurl:files.meetup.com.
Filling up the Kindle...
