Tim Leighton-Boyce brought this great little online service to our attention - it's a pay-as-you-go usability test service where testers are given specific tasks, such as "buy a red dress" or "find a gift for you mother" and the results & commentary are recorded...

We liked it so much based on a short trial on the Thorntons site, that we are blogging the company.
http://www.usertesting.com
It's $29 per one tester, with scale discounts for lots.