e-textbooks, what's out there?

Our district is about to make a middle school math curriculum purchase because our current curriculum is chopped and hobbled together due to differences in Math grade level expectations.  I have seen a brief presentation that Discovery Learning put together explaining their e-textbooks, but was wondering if any of you had experience or ideas about e-textbooks compared to traditional instructional books at the 6th-8th levels.  I am most concerned about access at home coupled with concepts that align with Michigan.  The common core will obviously streamline all of this soon, so one would think that the objectives are becoming more aligned from state to state.  Thanks,  Jeremy