Comcast does that on their password reset pages. E.g., go to https://login.comcast.net/myaccount/reset, type in "foo", and click "Next."

Edit: From checking the source, it looks like they're using NuCaptcha (http://www.nucaptcha.com/). Looks like O2, Groupon, and StumbleUpon are also NuCaptcha customers. You can see examples on this page: http://nucaptcha.com/features/security-features