We're planning to use FitNesse, with the RestFixture. We haven't started writing our tests yet, our newest tester got things up and running last week, however he has used FitNesse for this in his last company, so we know it's a reasonable setup for what we want to do.
More info available here: http://smartrics.blogspot.com/2008/08/get-fitnesse-with-some-rest.html