I believe that you saw a sphinx moth, also called a hummingbird moth, because it looks so much like a hummingbird. It is a diurnal moth, which is common in gardens this time of the year. You can see and learn more about this insect on the eNature Field Guide site at: http://eNature.com/search/show_search_thumb.asp?sort=1&curGroupID=99&display=1&area=99&curPageNum=1&searchText=sphinx+moth

