Depending on your purpose here are the options from the least reliable to the most reliable.
Online sites like Zillow.com or eppraisal.com both can be 10%-20% off but will give you a general idea.
A local agent can talk to you over the phone and based on your general description of the home and public records provide a CMA.
A local agent can visit and inspect your home and prepare a more comprehensive CMA.
You can hire an appraiser who for a fee will inspect your home and provide a detailed report with a valuation estimate.
Finally you can put your home on the market and see what a qualified buyer is willing to pay.