You are describing a Bold Jumping spider. Very common from the great plains to the east coast. Note the adults have white spots while the juveniles have the orange spots. Most easily Identified by the green/blue iridescent fangs or chelicerae. They are quite harmless, rarely bite humans and if they do, It only leave a slight redness and irritation.
A garden spider
I believe this spider friend of yours is a jumping spider, although there are lots of other spiders out there who are yellow, grey, black, orange and brown.
Ariel
A brown spider with a yellow stripe on its head is a wolf spider. The wolf spider may sometimes have an orange stripe on their head also.
Poisonous spiders are many different colors. The Black Widow is as the name states black with a red hourglass on the bottom of the abdomen. The Brown Widow is a light to dark brown spider that looks like the Black Widow only with patterns of brown. It too has a red hourglass on the bottom of the abdomen. The Brown Recluse Spider too is brown like the name states with a darker brown 'violin' marking on the cephalothorax. The Hobo spider is light brown with a darker brown abdomen and a cream colored strip going down the center of the cephalothorax. Yellow Sack Spiders are usually yellow or creamy colored. The Brazilian Wandering Spider is a dark brown spider and usually have red hairs on their chelicerae.
wolf
Spider is light brown with gold or yellow diamond back
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.
A spider that is brown with a large yellow belly might be a brown widow. Almost all spiders roll into a ball for protection. This spider could also be a garden orb.
A Garden Spider
Araneus diadematus Scroll down to see pictures of it when young with the yellow body and black spots: http://www.nicksspiders.com/nicksspiders/araneusdiadematus.htm -Michael Cline
the pupu spider
The spider that is black with a white crescent on its back is the Brown House Spider. This spider is often confused with the red-back spider.