Hi Laura,
There are two solutions as I see it -
1. Use list view in leads and the "Latest Leads" group which will show leads added in the last 30 days. As it is a standard group, all users should have access to it.
2. Using something like Orbis Alerts, automatic emails can be sent out to nominated users if no action has been taken on a lead after so much time.
I hope that gives you some ideas.
Ben