There are paid sites and you can create them yourself, but there are lots of free resources online that you can use as is or tweak for your specific use. Sometimes it is hard as we work at an Army chapel to find professional graphics for our slides and use in promoting our services. Many churches have staff that create material and want to encourage others by giving away their resources. They use the graphics at their church and realize that they can be used by others.
Find Free announcement slides and series graphics from various graphic designers and churches. Check out this article from church relevance.com
What sites have you used for resources at your chapel?