Amsterdam Hotspots
Hotels in all categories reviewed by guests.
http://www.amsterdamhotspots.nl/sleepbudget2.html

BUG
Read or contribute to reviews of Amsterdam hostels.
http://www.bugeurope.com/reviews/Netherlands/Amsterdam/

Channels.nl
A-Z of Amsterdam hotels, many of which include customer reviews.
http://www.channels.nl/cgi-bin/pagatoz.cgi?hotels

Euro Cheapo
Honest and independent reviews of budget hotels in Amsterdam.
http://www.eurocheapo.com/amsterdam/

Eurotrip
Shines a spotlight on the city's hostels.
http://www.eurotrip.com/hostels/netherlands/amsterdam.html

Hostelz.com
Carries reviews of all of Amsterdam's main hostels.
http://www.hostelz.com/view.php/Netherlands_North-Holland_Amsterdam_Hostels

Net4.com
Tells you what the guidebooks have to say about various hotels in Amsterdam.
http://www.net4.com/amsterdam-hotels/

Travel Intelligence.net
Detailed reviews, by professional writers, of hotels around the world including a number in Amsterdam.
http://www.travelintelligence.net/wsd/html/htlsbyplce.htm