Here is a superb infographic by Hannah Fairfield from the New York Times in 2010 - plotting the cost of a gallon of gas versus number of miles driven per annum by US drivers (HERE).
It is essentially a scatter plot - but because the unfolding of this relationship over time is relatively straightforward the designer has joined the dots. This gives a unique way of looking at the two variables per yearly data point.
The graphic is Copyright New York Times