A couple sites that have calendars of activities are Amanda Bennett and one from Disney. There are so many....just google summer calendar of kids activities!
My friend, Sarah, of Wildflowers Character Resources, has also created a list of frugal summer ideas from A to Z! You can find it in her May newsletter (sign up here and even download a free sample). For example, for the letter B she suggests creating fun with balloons, bubbles, and a big box! ...it's the simple pleasures of life, right?!!
What are some fun activities or ideas you want to share with us?