What are the standard ways of finding out how much a home is worth?

A comparative market analysis and an appraisal are the standard methods for determining a home's value.
Your real estate agent will be happy to provide a comparative market analysis, an informal estimate of value based on comparable sales in the neighborhood. Be sure you get listing prices of current homes on the market as well as those that have sold. You also can research this yourself by checking on recent sales in public records. Be sure that you are researching properties that are similar in size, construction and location. This information is not only available at your local recorder's or assessor's office but also through private companies and on the Internet.
An appraisal, which generally costs $200 to $300 to perform, is a certified appraiser's opinion of the value of a home at any given time. Appraisers review numerous factors including recent comparable sales, location, square footage and construction quality.