Some of the important cmd prompt commands :

Copy and keep it handy..

ADDUSERS --Add or list users to/from a CSV file
ARP -- Address Resolution Protocol
ASSOC -- Change file extension associations
ASSOCIAT --One step file association
AT -- Schedule a command to run at a later time
ATTRIB --Change file attributes

BOOTCFG --Edit Windows boot settings
BROWSTAT --Get domain, browser and PDC info

CACLS -- Change file permissions
CALL --Call one batch program from another
CD --Change Directory - move to a specific Folder
CHANGE-- Change Terminal Server Session properties
CHKDSK -- Check Disk - check and repair disk problems
CHKNTFS -- Check the NTFS file system
CHOICE --Accept keyboard input to a batch file
CIPHER --Encrypt or Decrypt files/folders
CleanMgr ---Automated cleanup of Temp files, recycle bin
CLEARMEM ---Clear memory leaks
CLIP ---Copy STDIN to the Windows clipboard.
CLS ---Clear the screen
CLUSTER ---Windows Clustering
CMD ---Start a new CMD shell
COLOR --- Change colors of the CMD window
COMP ---Compare the contents of two files or sets of files
COMPACT --- Compress files or folders on an NTFS partition
COMPRESS ---Compress individual files on an NTFS partition
CON2PRT ---Connect or disconnect a Printer
CONVERT ---Convert a FAT drive to NTFS.
COPY ---Copy one or more files to another location
CSCcmd ---Client-side caching (Offline Files)
CSVDE ---Import or Export Active Directory data

DATE --- Display or set the date
Dcomcnfg DCOM ---Configuration Utility
DEFRAG ---Defragment hard drive
DEL ---Delete one or more files
DELPROF--- Delete NT user profiles
DELTREE ---Delete a folder and all subfolders
DevCon ---Device Manager Command Line Utility
DIR ---Display a list of files and folders
DIRUSE --- Display disk usage
DISKCOMP--- Compare the contents of two floppy disks
DISKCOPY ---Copy the contents of one floppy disk to another
DNSSTAT ---DNS Statistics
DOSKEY --- Edit command line, recall commands, and create macros
DSADD ---Add user (computer, group..) to active directory
DSQUERY--- List items in active directory
DSMOD ---Modify user (computer, group..) in active directory

ECHO--- Display message on screen
ENDLOCAL--- End localisation of environment changes in a batch file
ERASE ---Delete one or more files
EXIT ---Quit the current script/routine and set an errorlevel.
EXPAND --- Uncompress files
EXTRACT--- Uncompress CAB files

FC--- Compare two files
FDISK--- Disk Format and partition
FIND ---Search for a text string in a file
FINDSTR--- Search for strings in files
FOR /F ---Loop command: against a set of files
FOR /F ---Loop command: against the results of another command
FOR ---Loop command: all options Files, Directory, List
FORFILES ---Batch process multiple files
FORMAT ---Format a disk
FREEDISK ---Check free disk space (in bytes)
FSUTIL --- File and Volume utilities
FTP --- File Transfer Protocol
FTYPE--- Display or modify file types used in file extension associations

GLOBAL --- Display membership of global groups
GOTO ---Direct a batch program to jump to a labelled line

HELP--- Online Help
HFNETCHK--- Network Security Hotfix Checker

IF--- Conditionally perform a command
IFMEMBER Is the current user in an NT Workgroup
IPCONFIG Configure IP

KILL Remove a program from memory

LABEL --- Edit a disk label
LOCAL --- Display membership of local groups
LOGEVENT--- Write text to the NT event viewer.
LOGOFF --- Log a user off
LOGTIME --- Log the date and time in a file

MAPISEND ---Send email from the command line
MEM --- Display memory usage
MD --- Create new folders
MKLINK --- Create a symbolic link (linkd)
MODE ---Configure a system device
MORE --- Display output, one screen at a time
MOUNTVOL ----Manage a volume mount point
MOVE --- Move files from one folder to another
MOVEUSER--- Move a user from one domain to another
MSG ---Send a message
MSIEXEC --- Microsoft Windows Installer
MSINFO ---Windows NT diagnostics
MSTSC --- Terminal Server Connection (Remote Desktop Protocol)
MUNGE --- Find and Replace text within file(s)
MV --- Copy in-use files

NET --- Manage network resources
NETDOM --- Domain Manager
NETSH ---Configure network protocols
NETSVC ---Command-line Service Controller
NBTSTAT --- Display networking statistics (NetBIOS over TCP/IP)
NETSTAT --- Display networking statistics (TCP/IP)
NOW --- Display the current Date and Time
NSLOOKUP--- Name server lookup
NTBACKUP ---Backup folders to tape
NTRIGHTS E---dit user account rights

PATH --- Display or set a search path for executable files
PATHPING ---Trace route plus network latency and packet loss
PAUSE --- Suspend processing of a batch file and display a message
PERMS --- Show permissions for a user
PERFMON ---Performance Monitor
PING ---Test a network connection
POPD --- Restore the previous value of the current directory saved by PUSHD
PORTQRY--- Display the status of ports and services
PRINT --- Print a text file
PRNCNFG --- Display, configure or rename a printer
PRNMNGR --- Add, delete, list printers set the default printer
PROMPT --- Change the command prompt
PsExec --- Execute process remotely
PsFile --- Show files opened remotely
PsGetSid --- Display the SID of a computer or a user
PsInfo ---List information about a system
PsKill --- Kill processes by name or process ID
PsList --- List detailed information about processes
PsLoggedOn ---Who's logged on (locally or via resource sharing)
PsLogList ---Event log records
PsPasswd --- Change account password
PsService --- View and control services
PsShutdown ---Shutdown or reboot a computer
PsSuspend ---Suspend processes
PUSHD --- Save and then change the current directory

QGREP --- Search file(s) for lines that match a given pattern.

RASDIAL ---Manage RAS connections
RASPHONE ---Manage RAS connections
RECOVER --- Recover a damaged file from a defective disk.
REG --- Registry: Read, Set, Export, Delete keys and values
REGEDIT --- Import or export registry settings
REGSVR32--- Register or unregister a DLL
REGINI ---Change Registry Permissions
REM --- Record comments (remarks) in a batch file
REN --- Rename a file or files.
REPLACE --- Replace or update one file with another
RD ---Delete folder(s) [remove dir]
RDISK ---Create a Recovery Disk
RMTSHARE ---Share a folder or a printer
ROBOCOPY--- Robust File and Folder Copy
ROUTE --- Manipulate network routing tables
RUNAS --- Execute a program under a different user account
RUNDLL32--- Run a DLL command (add/remove print connections)

SC --- Service Control
SCHTASKS--- Create or Edit Scheduled Tasks
SCLIST --- Display NT Services
ScriptIt Control ---GUI applications
SET --- Display, set, or remove environment variables
SETLOCAL--- Control the visibility of environment variables
SETX ---Set environment variables permanently
SHARE --- List or edit a file share or print share
SHIFT --- Shift the position of replaceable parameters in a batch file
SHORTCUT ---Create a windows shortcut (.LNK file)
SHOWGRPS ---List the NT Workgroups a user has joined
SHOWMBRS ---List the Users who are members of a Workgroup
SHUTDOWN ---Shutdown the computer
SLEEP --- Wait for x seconds
SOON --- Schedule a command to run in the near future
SORT --- Sort input
START --- Start a separate window to run a specified program or command
SU ---Switch User
SUBINACL ---Edit file and folder Permissions, Ownership and Domain
SUBST --- Associate a path with a drive letter
SYSTEMINFO--- List system configuration
TASKLIST--- List running applications and services
TIME ---Display or set the system time
TIMEOUT--- Delay processing of a batch file
TITLE --- Set the window title for a CMD.EXE session
TOUCH --- Change file timestamps
TRACERT --- Trace route to a remote host
TREE --- Graphical display of folder structure
TYPE --- Display the contents of a text file
USRSTAT--- List domain usernames and last login
VER ---Display version information
VERIFY --- Verify that files have been saved
VOL --- Display a disk label
WHERE --- Locate and display files in a directory tree
WHOAMI --- Output the current UserName and domain
WINDIFF --- Compare the contents of two files or sets of files
WINMSD --- Windows system diagnostics
WINMSDP--- Windows system diagnostics II
WMIC ---WMI Commands
XCACLS --- Change file permissions
XCOPY--- Copy files and folders