For fourth grade, from the big publishers you would be looking at Holt McDougal or McGraw-Hill if you are looking for interactive online versions either indepenently or to go along with textbooks/workbooks. The online versions have audio and teaching of concepts. Sadlier-Oxford would only have reteaching videos without audio.
For access to Destination Math and DOMA you could view their sites or check them out at
www.homeschoolbuyersco-op.org. They have some of them on group buys right now so there are trials available, or at least previews on some. Destination Math can also interchange with the Saxon Math texts so each could be used independently or in combination.
