I got a comment off of a review of a website service called 'Usabilla' on post I wrote regarding making money off of usability testing. Marcus (said commenter) having left NO email or reply but DID leave an Australian IP address, pointed out an Australian company called www.Loop11.com. And while it felt like he might be selling his own product I did check it out.
Much like Usabilla, Loop11 allows you to create your own tests, invite participants to interact with your materials and then you'll receive an assortment of returned data from the process. I'll say this, I'm glad to see that there are these services available to us and now you have some companies to compare.
A few more companies for your consideration set:
This is a must read:
And for your consideration here's 'A List Apart Article' on "The myth of Usability Testing." I'm just trying to stay objective here people.