I've been assigned to research out and spec replacing our old and decrepit http content filtering system. There are several open source filtering packages available but I've not come across one that does SSL inspection.

The new system will scale to many branches of different sizes, from say 10 users to a few hundred, so purchasing an appliance for each branch isn't desirable.

When we're further along, we will do custom programming as we have a few unique needs in other aspects of filtering, so if the suggestion takes a bit of customization, it won't be a problem.