Following are some useful Unix/Linux commands which are helpful if you are dealing with large sites (files and db size). I find these really handy when moving sites from one server to other, taking backups of Files, Database etc.
Note: To get access to the Unix command line, you will need an SSH client (e.g. Putty). You can also use WinSCP if you are not comfortable with Command line. WinSCP has a feature to enter custom commands using its interface.
Please add other command-line commands that you use while setting up, developing and managing your Drupal sites.
Zip Contents of current directory
zip -r zipfile.zip *
Unzip Contents into current directory
Unzip (and extract) the tar'd, gzipped archive (tarball) Contents into current directory
tar zxvf tarballfile.tar.gz
Remove a directory and its contents (Use with extra care)
rm -rf directoryname
mysqldump dbname -uUSERNAME -pPASSWORD --host HOST > filename.sql
mysql -u root -p[root_password] [database_name] < dumpfilename.sql
Copy all files / directories from one server to other (Both servers should have SSH Support)
rsync -avz --progress username@servername:sourcefolder destinationfolder
Drupalize.Me offers a series of free videos on leveraging the command line in Linux/Unix/OSX for Drupal...
Moving Around the Command Line
Copy, Move and Delete on the Command Line
Dealing with Permissions on the Command Line
Creating Symbolic Links on the Command Line
Using Zip and Tar from the Command Line
Finding Files from the Command Line
Grep is your friend
Using Shortcuts from the Command Line
Setting Aliases in the Bash Shell
Working with the MySQL database
Using SSH and SCP to Access Remote Servers
Drupalize.Me also has a whole series of free videos on working with VI/VIM -- an extremely powerful text editor that is available on virtually all flavors of Unix/Linux/OSX systems...
Intro to the VI/VIM Editor
Editing Documents with VI/VIM
More Editing Tricks with VI/VIM
All About Shortcuts in VI/VIM