Well, for a clearly reformist website you can check out the Heritage Foundation's 'Social Security Reform Center'.
It's amazing to see how much spin this issue is generating. Everyone is busy pushing their agenda and using inflammatory statements. For example, many people describe Social Security as bankrupt because in thirty or forty years it can't pay benefits as paid today. This is a rather interesting definition of bankrupt. Similarly, some of the retirement-oriented websites are squawking about how there is no crisis and there's plenty of time to reform things later (especially since the audience they are targeting will be dead by then, I suppose).