Perhaps Zillow’s Z-estimate is worthless (I’m not sure why people pay so much attention to it), but the rest of Zillow is very good.

I use it frequently to determine property lines, last sales date and price, and see bird’s eye view of the neighborhood. Used in conjunction with Google’s Street View, there is a wealth of data you can collect about a property from the warmth of your own room – something not possible 2 short years ago.