If you're looking for unmoderated remote user testing, the choice of services at the moment can be overwhelming. This article goes through the different types of services available and lists a few companies you might want to try.
Personally, I've found one service that works for me and stuck with it, but there are other approaches and opportunities I need to try out when the right project comes up. I think this is a good starting point for further investigation.
How to Shop for Unmoderated Usability Testing Tools - article by Bill Albert on johnnyholland.org
Previous blog post: Usertesting.com - big thumbs up (November 2009)