Standard PCB trace widths?
You can use this nomograph to determine the width according with current:



Using the nomograph


Locate the width of the conductor on the left side of the bottom chart.
Move right horizontally, until you intersect the line of the appropriate conductor thickness. Move down vertically to the bottom of the chart to determine the cross-sectional area of the conductor.
Move up vertically, until you intersect the line of the appropriate allowable temperature rise. This is the increase in temperature of the current-carrying conductor. Conductor temperature should not exceed 105°C. For example, if the ambient temperature might reach 80°C, the temperature rise above ambient of the conductor should be less than 25°C (105°C - 80°C). In this case use the 20°C curve.
Move left horizontally, to the left side if the chart to determine the maximum allowable current.


Reverse the order of these steps to calculate required conductor width for a given current.

More informations at this site: http://www.minco.com/products/flex.aspx?id=1124

This graph is from IPC, but I cannot find it there.