Green Alternative to Toilet Paper?

Excuse us while we go all Sheryl Crow on you, but we've been wondering what kind of alternatives to toilet paper there might be. We've been a bit stumped looking for statistics on how many trees are felled annually to make a product that is designed to be thrown away, but we did find these numbers, culled from the trustworthy Euromonitor report. They show that Americans use more than 50 pounds of toilet paper per year. That's almost twice as much as Europeans use.

We're not suggesting that everyone go back to corncobs and outhouses, but wider use of bidets (or bidet retrofits, like Toto's washlet) would surely help cut back on this waste. However, bidet use alone can't explain the discrepancy in use between Europe and the US: we know from experience that not every European home has a bidet. Either they use the bathroom a whole lot less than us, or our friends across the pond must just use fewer sheets to do the job. Aside from Sheryl's widely ridiculed suggestion that a law be passed to limit use to one or two squares, what else could be done to stem the flow of TP?