Check out Pex for Fun (http://bit.ly/PexLearn) for a challenging and engaging way for students to practice their programming skills. Pex for Fun enables programming in C#, Visual Basic, and F# right within the web browser.
Students can write your own code and immediately check the results in order to:

The Coding Duels add another level of engagement with interactive puzzles in which the task is to implement the Puzzle method to have exactly the same behavior as another secret Puzzle method. There are over 200 of built in puzzles and coding duels, many rated by users.
On the site you will find instructional video tutorial and plenty of teaching resources. There are even a few short “courses” that keep track of student progress as they learn C# and other CS concepts. The course starts with the traditional Hello World program and guides you through the language constructs all the way to Exception Handling.
All and all, a worthwhile browsing, playing, and learning activity for CS students.
Pat Phillips
Editor, CSTA Voice