defrag
You probably already guessed that this defrags your hard drive. Type only "defrag" into your command prompt to get a list of possible arguments, such as the drive letter and the type of output.

diskpart
Manages your disk partitions. After you type "diskpart" into your command prompt, your prompt will become "DISKPART." Type a question mark to get a list of possible arguments. Type exit to leave diskpart.

driverquery
Will get you a nice list of your drivers and their properties.

fsutil
This is a handy command. You can do everything from managing your hardlinks to querying the free space in a volume. Type "fsutil" into your command prompt, and you'll see a list of options. I choose "fsinfo" from the list, so I type "fsutil fsinfo" into the prompt. Now I get even more options, but I choose drives by typing "fsutil fsinfo drives." It's fun, it's easy, and you'll get the hang of it. Explore this utility. There are a lot of cool features and hidden twists.

getmac
This gets the MAC (Media Access Control) address.

gpresult
Get the RSoP, user settings, and computer group policy settings.

netsh
A network configuration tool. Type "netsh" to enter the tool, or "netsh /?" to learn more about it. To exit this tool, type "exit" at the "netsh>" prompt.

openfiles
Allows an administrator to display or disconnect open files in XP professional. Type "openfiles /?" for a list of possible parameters.

recover
This command attempts to recover readable information from a damaged disk. Type "recover" to get the syntax.

reg
The console registry tool. Get syntax help when you type "reg" into the prompt. You can export the registry, copy, restore, compare, and more.