CodingBat - A great site to complete short, simple programming problems in both Java and Python. Create an account to keep track of your progress!
JEliot - Great way to "see" your code in action!
Mobile App Development
MIT App Inventor (web-based)
APCS Multiple Choice Questions - Hosted by Georgia Tech, this site will generate a random question similar to the ones given on the AP Computer Science exam.
Made With Code - Google's initiative
NCWIT - National Center for Women & Information Technology
Camps, Academics, and Seminars
Contesting & UIL Computer Science