I think the best way for someone to really learn something is to be able to teach others and explain why something is the way it is.
A good tool for that in a team environment is a Tech Talk, and it can be as formal or informal as your team. Have someone present in whatever manner they choose to the team on a topic they're passionate about.
Your Area of Responsibility
Tips, Tricks, and Tools - How do you get things done?
Your favorite new tool/library and Why
Sell Me Your Product
New Technique, Best Practice
Program Management Overview
Leadership Development and Counseling Tactics
Your Side Project, Technical or Not
97 Things Every Programmer Should Know - Pick/Assign One Each
Operations / IT Infrastructure 101
Business processes and procedures