Googling around, my best guess is that the species is Araneus gemmoides, commonly known as a cat-faced or jewel spider. These are orb-weaving spiders that can get pretty big, and they usually build their webs around porchlights.
Hopefully she'll take care of some of the critters that are chomping on the hostas. If she hangs around and starts spelling some words in her web, I'll post those too.
