My lease will expire on 8/28/12. I have found a new place. I will deliver a 30-day notice to leave on 8/11/12. My current lease states that I will have to pay on a month-to-month basis (at a higher rate) for the entire month, starting on 8/29/12 and running to 9/29/12, regardless of when I move out. Is this legal? Would I have to pay a whole month of month-to-month rent even if I move out before the month ends on 9/29/12?

ANY question on law needs to include your general locale as laws vary by area.

But its likely legal. Not all area allow pro-rating. Some areas require notice be 30 days prior to the end of the rental period. Since you did not give notice 30 days prior to 8/28, then the month to month provision kicks in and you are responsible for another month.