What design will we have on the quarter after the State Quarters program is finished?

I don't know for sure.

The only information I've been able to find was on this Wikipedia entry.

"Congress in recent years has ordered the Treasury to redesign the Lincoln cent, Jefferson nickel, and Sacagawea dollar; also, many supporters of the dollar bill say they wish to preserve Washington's memory, and they would be equally opposed to removing him from the quarter. Thus, the odds of Washington disappearing from the quarter after 2009 are all but nonexistent, though a redesign is possible (as with the cent and nickel)."