Try these tables if you really want an accurate answer. Rule of thumb would be 12-14 AWG for normal household outlets up to 30 amp and reasonable length. The problem you will find here is not the size of the conductor but the pissy quality of the conductor, poor insulation, and terrible terminations. Of these all you can typically fix is the terminations if you are comfortable stripping wire. Please don't electrocute yourself. They have plenty of 'electricians' here who will work hot circuits and kill themselves for a measly fee.
Try these tables if you really want an accurate answer. Rule of thumb would be 12-14 AWG for normal household outlets up to 30 amp and reasonable length. The problem you will find here is not the size of the conductor but the pissy quality of the conductor, poor insulation, and terrible terminations. Of these all you can typically fix is the terminations if you are comfortable stripping wire. Please don't electrocute yourself. They have plenty of 'electricians' here who will work hot circuits and kill themselves for a measly fee.
Calculator:
http://www.csgnetwork.com/wiresizecalc.html
http://www.powerstream.com/Wire_Size.htm