Bruegel just published this briefing paper which I prepared a few weeks ago at the request of the European Parliament's ECON (Economic and Monetary Affairs) committee. In it, I argue that the information and reference privileges currently enjoyed by credit rating agencies should be dismantled to establish a fairer competition with other financial risk assessment services providers. This is far more important than regulating the agencies themselves.
Download BruegelPolicyContribution_Feb09_Ratings in case the above link does not work.