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You can try namepros. It’s a forum where people actively appraise domain values. http://www.namepros.com/domain-appraisals/
Keep in mind that these are really only guesses, and the valuation can vary widely for any given domain. In the end, the only real value is what someone is actually willing to pay. For example, a hypothetical domain named bigfishdoghouse.com would have very little value...except to the guy who just started The Big Fish Doghouse Company.