vim

:%s/old/new/g	Replace all occurences of old by new in file
:%s/onward/forward/gi	Replace onward by forward, case unsensitive
:%s/old/new/gc	Replace all occurences with confirmation
:2,35s/old/new/g	Replace all occurences between lines 2 and 35
:5,$s/old/new/g	Replace all occurences from line 5 to EOF
:%s/^/hello/g	Replace the begining of each line by hello
:%s/$/Harry/g	Replace the end of each line by Harry
:%s/onward/forward/gi	Replace onward by forward, case unsensitive
:%s/ *$//g	Delete all white spaces
:g/string/d	Delete all lines containing string
:v/string/d	Delete all lines containing which didn’t contain string
:s/Bill/Steve/	Replace the first occurence of Bill by Steve in current line
:s/Bill/Steve/g	Replace Bill by Steve in current line
:%s/Bill/Steve/g	Replace Bill by Steve in all the file
:%s/^M//g	Delete DOS carriage returns (^M)
:%s/\r/\r/g	Transform DOS carriage returns in returns
:%s#<[^>]\+>##g	Delete HTML tags but keeps text
:%s/^\(.*\)\n\1$/\1/	Delete lines which appears twice
Ctrl+a	Increment number under the cursor
Ctrl+x	Decrement number under cursor
ggVGg?	Change text to Rot13