This is a female huntsman spider. The white, pillow-like object under the body is her egg sac. Each egg sac can contain over 200 eggs so you are likely to see more of them. Huntsman spiders are not poisonous, but can bite if handled. They can be considered beneficial since they feed on cockroaches and other insects, but are frightening to some people due to their large size and the speed with which they can run.

More information on the huntsman spider can be found at:

Additional Resource
http://edis.ifas.ufl.edu/in317