Willer offers a bus pass that allows up to two long-distance bus trips per day for 3, 4 or 5 non-consecutive days:
http://willerexpress.com/x/bus/dynam...ml/pc/buspass/

I don't think we've discussed it in detail in the Japan forum, but it's been mentioned in the budget travel forum:
http://www.flyertalk.com/forum/budge...an-budget.html

It works very differently from the rail passes, which allow you to hop on and off as many trains as you like, with or without reservations. I might think of this as a discounted set of tickets rather than a "pass" as such. So you need to read the Ts and Cs quite carefully to make sure it works for you. If it does, I think it should be a very attractive proposition for budget travelers who want to go long distances in Japan. The fact that it can be used on non-consecutive days makes it particularly useful - as you can see from the example itineraries:

http://willerexpress.com/x/bus/dynam....../course.php