Well no so much a utility as a setting I suppose. What is it? It is OpenDNS. What does it do? It allows you to point your DNS to much bigger, faster, better featured, highly reliable, etc service for retrieving the domains you type into your web browser. Why is it better? Well apart from being all the things I just mentioned it allows you to monitor all your DNS requests, for all your networks from a web console (cool). Also, it can be configured to prevent requests to phising and "adult content" web sites. This means that if a user inadvertently clicked on an email that contained a link to a phising site (to obtain their banking details for example without them knowing) then the request would be automatically dropped and the user would get a nice warning page.
By using OpenDNS on your network you'll ensure that not only will your users get a faster response to their request for web sites but they'll also be better protected. Even better you can access all you DNS statistics from a web console and lots more features. To cap it all off OpenDNS is TOTALLY FREE! So there is no reason not to use it.
Take a look at OpenDNS and I think you'll find that it has plenty of really cool benefits for a price that is hard to match.