get the regular instrument rating test prep book from ASA. its almost if not exactly the same test bank. if your gonna take that also take the IGI test which again is almost exactly the same test bank.
the other option would be sheppard air. have heard good things about all their software but never used it myself. they guarantee 90% or your money back. A coworker of mine got an 88% on his ATP and they had the money back in his account the next day