What type of spider is this and is it harmful?
This is a giant house spider. In spite of its very large size -- up to 4 inches across, toes to toes -- it is not dangerous to people or pets. It belongs to a large group of spiders, the Agelenidae.
See 'Giant House Spider' - http://pestsense.cahnrs.wsu.edu/Search/MainMenuWithFactSheet.aspx?CategoryId=2&ProblemId=842.