As good a place as any

This is as good a place as any to note down a few linux commands I always manage to forget:

• How to untar afile.tar
• tar -xvf afile.tar
• How to untar and unzip afile.tar.gz
• tar -xvzf afile.tar.gz
• How to see how much memory is taken up by certain directories or what not
• du
  
• du -h (Human readable - using K and M)
• du -m (Gives size in Megabytes, M)