The Commands from the Emacs Reference Card
that I have found to be the most useful.

C-z    	    Suspend Emacs
C-x C-c	    Exit Emacs permanently

C-x C-f     Read a file into an Emacs buffer
C-x C-s     Save contents of buffer back to disk
C-x C-w     Save contents of buffer to specified file

C-g 	    Abort partially typed or executing command

C-_ 	    Undo most recent change

C-s	    Search forward
C-r	    Search backward
(repeating either of these repeats the search)

C-v	    Scroll to next portion of buffer
M-v	    Scroll to prev portion of buffer
M-<	    Scroll to beginning of buffer
M->         Scroll to end of buffer

C-d	    Delete next character
C-w 	    Kill region (see selecting mark/region below)
M-w	    Copy region to "kill ring"
C-y	    Yank back last thing killed
M-y	    Replace last yank with prev kill

C-SPACE	    set "mark" here

Note about selecting mark/region.
  When cursor subsequently moves, the "region" is defined as
  that portion between the "mark" and the current cursor position.
  So, setting mark at beginning of buffer, then scrolling down
  three lines, and then doing C-w will kill the first three lines.

M-%	    Interactively search and replace
              When active, SPACE replaces current item
	      and searches for next one.  ! replaces all
	      matching items.

C-x 1	    Delete all other windows.
C-x 2	    Split window into two
C-x o	    Switch cursor to another window

C-x b	    Select another buffer
C-x k       Kill a buffer

M-x shell   Start a shell in a window called *shell*

TAB 	    indent current line

In the MiniBuffer at the bottom:
  TAB   complete as much as possible
  RET   complete and execute
  
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In Lisp buffer:

C-c C-p   scroll through previous Lisp expressions
C-c C-n   .............. next ....................