vim

Vim is a highly configurable text editor built to make creating and changing any kind of text very efficient. It is included as "vi" with most UNIX systems and with Apple OS X.
Basics
v visual mode
i insert mode
:w Save file
:x Save and exit
:q Exit if no changes have been made
:q! Exit and undo any changes made
:set nu Display line numbers
Navigation
h / j / k / l left / bottom / top / right
gg Goto top of doc
G goto bottom of doc
w goto next word
W goto next word past punctuations
b goto start /back/ of word
B goto start /back/ of word past punctuations
e goto end of word
{ Move back one paragraph
} Move forward one paragraph
^ goto the beginning of the line
dollar sign goto the end of the line
G goto the nth line
% Move to the matching bracket
Deleting
x Delete a single character
D Delete the rest of the line
dd Delete the entire current line
ndw Delete the next n words
ndd Delete the next n lines
:x yd
Cut and Paste
p Paste the clipboard contents
yy Yank /copy/ a line
yw Yank a word
y dollar Yank to the end of the line
Search and Replace
/pattern Search forward
?pattern Search backward
n Find the next occurrence of pattern
:%s/pattern/replace/g Replace every occurrence of pattern with replace