ePinions
Offers trip reports from people who have visited Amsterdam already.
http://www.epinions.com/trvl-Dest-Europe-Netherlands-Amsterdam

Rick Steve's
Offers a wealth of hints and tips from travellers on a host of subjects related to travel in Europe.
http://www.ricksteves.com/graffiti/home.htm

Thorntree
A travel forum with lots of tips for anyone heading for Holland or anywhere else in Europe.
http://thorntree.lonelyplanet.com/

Virtual Tourist
A web forum where you can get answers to any Amsterdam-related questions you post.
http://www.virtualtourist.com/vt/71211/