Always see this when walking the dog. Clusters of white hanging flowers with five-pointed leaves. What is it?
SOLVED: Hanging Cluster of Flowers?
Yes, and that's the double-flowered one: Hydrangea quercifolia Snowflake™
ViburnumValley definitely has it right. The only double flowering oakleaf hydrangea until recently (I think Proven Winners came out with the Gatsby series - check Gatsby Star for their double flowering oakleaf). There are some others but I don't trust the sellers on those.
Make sure you buy it in bloom if you want 'Snowflake'. Slower growing than other oakleaf hydrangeas but worth it.
Here is a picture of mine from last summer.