KhanAcademy: Rate Problems 2 Quia: Battleship (flash) 

MathScore: Work Problems Quia: Challenge Board (flash) 

Mesacc: Work Problems Quia: Challenge Board 2 (flash) 

Resources

Algebra.com: Joint Work MathOnline: Work Problems- More than 2 Persons 

BasicMathematics: Working Together MathOnline: Work Problems 2 

CliffsNotes: Work Problems MathOnline: Work Problems- 2 Persons 

MathGuide: Work Problems Mesacc: Work Problems 

MathOnline: Work Problems PurpleMath: Work Word Problems