Use Agents and Appraisers
After getting a ballpark estimate, it's time to ask the experts. And why not? It's free. Listing agents need your business, and one of the things they do to get it is offer a free walk-through and a Comparable Market Analysis (CMA). A CMA should include carefully selected comparable properties, a listing of the factors that make your house unique and an analysis of current market conditions. Consider getting at least three CMAs from three different agents.
But keep in mind that while they may certainly be friendly, real estate agents aren't necessarily your friends. They need to make money, and to make money, they need to get your listing. To get your listing, an agent may be prone to offering an unrealistically optimistic listing price, imagining you'll choose the agent who thinks he or she can get the best price. If an agent's suggested listing price seems too good to be true, it probably is.
Instead, you might go straight to an appraiser. Appraisers are impartial, but you'll have to pay for this clear-eyed opinion. However, in addition to getting a price, having your home appraised before putting it on the market allows you to fix things that could slow a sale or even update things that could get you a better selling price. Talk to your appraiser to see what he or she thinks could make your home more valuable, and then follow through with the appraiser's suggestions.