I am working in a financial institution(Dad luck me:-（), which involved strict permission or security policy and enforcement. SharePoint build-in permission feature is not good at all to me since it is just present simple permission options.
We also hired a consultant who did some enhancements to us. Yet the most impressive thing is a tool called <a href=”http://www.sharepointboost.com/permissionboost.html”>SharePoint Permission Boost</a>. With its rich features, many complex permission requirements can be solved.
Also a tool called <a href=”http://www.sharepointboost.com/columnpermission.html”>SharePoint Permission Boost</a> is also very impressive.
Hope this helps