I think now it is relatively common knowledge that ladybugs are an important insect species or beneficial insects for the garden because they eat pest insect species.  But, I bet you didn't know there are about 500 species of lady bug in the United States alone..  In my garden they all look the same.  Now, I'm going to have see if I can tell them apart when I see them.

From Birds and Bloom:

10 Things You Didn't Know About Ladybugs