It's been mentioned here and there, but
http://www.sexjobs.nl/ looks like a great site for finding independent providers in Amsterdam and the rest of the Netherlands. One thing I noticed is that a lot of the women making themselves available there are actual Dutch women. I'd imagine it's more difficult for a girl from Romania (for example) to set herself up and work via sexjobs.nl than the windows.
If folks have any stories regarding sex jobs.nl I'm sure others would like to hear them. Please consider adding them here.