FreeTech4Teachers.com. One of those is iPadApps4School.com to which I have applied some lessons that I learned from making mistakes with this blog. One of those mistakes was not making it easier to sort resources according to grade level.
On iPadApps4School.com you can sort app reviews according to grade level category. Simply click on the grade level category in the sidebar to find apps appropriate for the age of your students. You can find elementary school apps here, middle school apps here, and high school apps here. I also have a category for pre-K students. If you want to be notified when a new app is reviewed, you can subscribe to email updates for iPadApps4School.com.