I recently learned of a fantastic site with many resources for your Problem Solving needs.
The site is Illustrative Mathematics, and can be accessed by clicking here. Definitely one to bookmark on your teacher computer!
Illustrative Mathematics is full of problem based tasks, broken up by grade level and standard. You can print the problems along with solutions, and once you print them you can keep them for years to come. Definitely a great resource for your Problem Solving station or just to have in your classroom.