We use Smart Filter by Secure Computing. Once you force authentication within ISA, you can created groups and policies which is very useful. With each policy, you choose the categories that users/groups are allowed to access. You can even set the times and days these categories are allowed/denied. Based on which group you are in will determine which sites you can view. Smart Filter vr 4 even comes with its own reporting tool which gives you a detailed report on your users whereabouts. We have been using it for over 4 years and have been very pleased.