Your Realtor has all this information through the various multiple listing services.
Realtors provide you a comparative market analysis of homes in your area; this will include a comparison of all the amenities in your home - next to "like" properties that have sold within a determined amount of time. The Realtor will typically include homes "for sale" as well - this makes the information up-to-date and keeps things on an even keel.
It depends on your area. If you contact a Realtor, this informationis available in the Multiple listing service. It will be in your county tax assessors web site, but many seem to take a couple of months to get posted