Nifty free networking tool Paglo Crawler identifies every device on your network--and gives you a great deal of information about each. Because it's somewhat confusing to decipher, it's not that well-suited for networking newbies. But if you know you way around a network, you'll appreciate the level of detail it offers. For example, for each device, you'll be able to view information such as its Netbios name, DNS information, network subnet, and even details about port numbers.
Note that in order to get information about your network you'll have to set up a free account with Paglo after you run the software; you view network the information over the Web, and need to log into your account to view it. There are also for-pay subscriptions available that give you access to more information than the free account provides.