We use an internal evaluation comprised of a drive-by, pulling tax assessed value and then pulling another value source, such as Zillow. So far, we haven't had any issues with the examiners on this method.
"So far" is the pertinent statement in this sentence. You need to read the 2010 Appraisal and Evaluation Guidelines very carefully regarding the development of an evaluation. Unless you have validated Zillow or your tax assessments to actual market values according to the guidelines, those resources are absolutely worthless in an evaluation.