try this also:
www.europebyair.com
klm also has a pass with one or two others (passport to europe?) - but often it is better to call the airlines directly because it is very difficult to get good info on it. also try www.opodo.com to see if you can get better fares. For cheap flights from ams - check the schiphol.com/.nl website - it has links to discounters operating from the airport.