Numberphile shows how to sign up to a trillion in one video. (Sign , not count --- you don't have time to count that high!)
The one I came up with used both hands. Each finger on one hand has 9 points - three on the left side, three on the middle surface, and three on the right - which were the values 1-9. The fingers of the other hand indicate the point, by touching the point. If the value is 0 then there's no touch.