Zillow.com and EAppraisal.com can give you a rough idea, but they are only approximates. If you are planning to sell you need to have an agent look over your home and provide a Comparable Market Analysis. We do this for free in anticipation of earning your business.
The other option you have is to hire an appraiser. Appraisers will provide a detailed analysis of what other similar homes have sold for and compare those to yours adjusting for various factors. An appraisal or CMA are not guaranteed selling price. They are a snapshot in time, based on reasonable assumptions. Time, market exposure and competition will determine your final selling price. I hope this was helpful.