What you get to keep in a chapter 7 (and to some extent how much you have to pay out in a chapter 13) is determined first by knowing the value of the assets you own. From the value you subtract any secured debt and any exemption which you have claimed in your property as part of the case.
Your valuation is not determinative nor is the Trustee's. If there is a dispute it is up to the Bankruptcy Judge to decide. Having said that, below are several good websites which you can use to get a good feel of what certain property is worth.
Cars, motorcycles, snowmobiles and watercraft
Kelley Blue Book
Houses
Bank of America
Realestateabc.com
Zillow
http://www.kbb.com/
http://bankofamerica.cyberhomes.com/searchresults.aspx?uniqueid=0
http://www.realestateabc.com/home-values/WA/Seattle/0989A88555DBBC9DE50CB9D341FED8CD
http://www.zillow.com/wiki/RealEstateWiki.htm