If you want an unbiased and accurate assessment, try looking at DenverPropertyValue.com Yes it's a realestate website, but it's free and will give you all kinds of currently listed and recently sold comparable homes. The big thing I really like is all the graphs and breakdowns. The biggest thing you want to watch is the asking -vs-selling price statistics.
The best way to determine your homes value is to find 3 similar properties that have sold in the past 6 months. Similar in size, location and condition. Boulder Real Estate Pro Jason Burch. http://www.boulderopenhouses.com
An appraisal is probably the most accurate. You can also look at comps which are similar properties that have sold in the past 6 months. I would be happy to send some over if you would like. Let me know. You can reach me at 720-352-9038 or firstname.lastname@example.org