For social studies classes, maps are always an effective activity for students at every level. You can hand a map out at any point of a unit and instruct students to fill it out to the best of their ability. Similar to the exit slips, you can instruct students that they are to fill the map out from memory or use their textbooks or notes to complete it. By using a map as a sponge activity, the students will always have a completed map to use for studying for the test you give them at the end of the unit. Maps are also always found on the MSA and HSA tests, so that will also help students get prepared. If you find yourself at the point where you need to use a map as a sponge activity, you can give students a minimum of how many countries or areas they must label before leaving. These maps can be considered as in-class participation or classwork for grading purposes.
The internet is a great resource to find maps. Here is a site that is ideal for finding maps on any area of the world. They are blank outline maps that students can fill in and color. The site is very easy to use; all maps are listed by continents.