Network Scanner by LizardSystems is a great tool that scans your entire network, then gives details about everything it finds: the IP address of every device, and important information about each.
The information it uncovers is especially useful for security purposes. For each computer (PCs as well as Macs), Network Scanner reports whether remote administration is enabled, and lists any folders that are shared publicly. That way, network administrators can quickly identify security holes, and close them on individual computers.
On my network, Network Scanner by LizardSystems was able to see every single device, including several PCs, a Mac laptop, home server, wireless router, and even a Motorola Xoom Android tablet. It didn't give details about the router or tablet, but that's because there was no information to give. They don't allow remote administration or have any shared folders.
There's only one drawback to Network Scanner: its price. At $40 for businesses, it's only for those who truly need it for work. But those who do need it for work will find the pricetag to be well worth it in saved time and peace of mind. And for non-commercial users, it's free with registration, so it's fine to use it on a home or non-profit network.