PUB400.COM provides free access to an IBM i 7.5 partition for educational purposes. Anyone can request a user profile for access. You can use this partition to improve your IBM i skills in general, program in CL, RPG, COBOL, and SQL, and learn web technologies.
This is the IBM i Community pages from IBM. You will find blog posts, articles, and discussion forums.
PowerWire published IBM i, AIX, and Linux news on its web site. You can also subscribe to their monthly newsletter.
Scott Forstie, Db2 for i Business Architect, has a gists page where he publishes useful SQL examples.
The IBM i Reference Pages community web site is filled with useful references.