Adding an item a certain amount of times
Example: Css comments /***/. Display 20 * across

    20i*<Esc>

Adding an item a certain amount of times separated by a charcter
Example: An array of 11 letter "0"s

    11io,<Esc>x

Basically its the same as outputting a certain amount of characters, just hitting x at the end to take out the last character.

Search and Replace 
  * :%s/foo/bar/g (% searches all lines, without % searches current line) 
    Find each occurrence of 'foo', and replace it with 'bar'
  * :%s/foo/bar/gc