Estimating Real Estate Appreciation

[James McHugh]

Is there a good authority website that allows you to properly estimate appreciation over say, a 5 year period in a specific zip code?  For example, I am using Zillow.com.  I have a house I'm looking currently for sale that sold 5 years ago for 129k (Zillow priced the real value at 170K for that period in time - why the big difference?)  AND at the time the average for that zip code was placed at 149k.

Now, it's listed for 199k, with Zillow saying it's worth about 193k and average for the zip code is 169k.  Forecasting for the next year says the appreciation is mostly flat, perhaps a tiny increase of a few thousand dollars.  

Am I going about evaluating this the right way or should I be using other methods?  Looking at it's last sale price to what it's listed at now, there's no way it appreciated about 80k or 54% when that zip has only appreciated on average about 13%.  Any pointers for this newbie?  Thanks!