If you haven't checked out the Marketing Experiments Web site yet I highly recommend it.

They're recommended by both Marketing Sherpa (another simply awesome resource) and the international multimedia news agency Reuters.

I have participated in live Web events they've sponsored and am really seriously considering attending their Expert Certification course next month.

I don't care about having certifications but I do care about learning from very sharp people with exceptional skills and quality testing programs. Exposure to any of their information will make it obvious that they know their stuff.