A tip: search listings on
ebay or Delcampe by price - order your results by most expensive first. This way you can usually find out which stamps are the most highly sought after by collectors. If you have thousands of stamps, then you're bound to have something that falls into this class.
Here's just one example: a search of Czechoslovakian stamps on
ebay with a price of above $200 revealed that this stamp has a 'Buy It Now' price of $400:
http://cgi.ebay.com.au/Czechoslovak...em414a6c2248Maybe you've got one too!