I assume your talking about the common garden spider: the spider in question is most likely the black and yellow Argiope (Argiope aurantia), one of the species of orb weavers. They are found throughout the North America (where ever there is a warm but not overly hot summer).
It is not likely to bite you but if you forced it to bite you by pressing it against your skin for some amount of time, the bite would result in swelling and discomfort. It would be a severe and unusual allergy that would result in anything more life threatening from a garden spider bite. they should be seen as a welcome site in any garden if you choose not to use insectisides as these will cut down on grasshopper populations in a very big way.
Brown recluse
Argiope aurantia, or the black and yellow garden spider, lives in California and has two yellow stripes running lengthwise down its back. They are not dangerous to humans.
grass spider
No, its acutally not harmless i did months of research.
Sounds like the "Garden wolf spider".
red back spider
brownrecluse
either its a new spider species, or its just a make believe spider!!
a very cute spider
Arachnic
a garden spider
i dont know for sure but i saw one in my back yard i dont know for sure but i saw one in nixa mo
What ya got there is a spiny-back spider. See Related Links for some pics.