I've not used the Yahoo! Real Estate service before, but this post to the Yahoo! Search blog perked my interest...Yahoo! has integrated a few of it's services with Zillow to give you instant home valuations of any address in the US.
A map of the area is displayed using Y! Maps beta technology (so you can move it around \ zoom \ switch to satellite) that displays comparable homes in that area - but you don't get the 'Bird's Eye View' option that you get from Zillow's mapping (it uses Windows Live Local for that)
The Yahoo! team have also added a new Y! Shortcut - type in 'home values' into a Y! Search bar and the first entry will allow you to input an address to lookup.
I've played with Zillow before - it's quite a bit of fun comparing your house to those in the neighborhood, it's also scary just how much information they have on you.
