This is just a scratch pad of links at the moment. I spent time playing with 'allworldstamps' and it looked like something I could use, but kept telling me a needed to register to get the rest of the features. What I did not fully appreciate was that it has been replaced by 'mycollection' which seems to have lost some of the important features. For my own collection I need to manage stamps in their various sets, something which 'allworldstamps' said that I needed to register to use, but 'mycollection' simply looses anything to do with sets of stamps. Since the bulk of my active collection is presentation sets and first day covers, not being able to catalogue them is something of a problem! SO now I am looking to an alternative method of cataloging them.
On-line catalog links
http://www.briefmarken.de/datenbank/index.php?_SPRACHE=EN ( Chargeable )
http://www.allworldstamps.com - being replaced by service below - but it's not as good!
http://stamp-valuations.co.uk/stampvaluation/valuation.html( Chargeable )