my favorite GNU commands:

Exit Emacs C-x C-c 
     save-buffers-kill-emacs 

Open a file C-x C-f 
  find-file 

Save a file C-x C-s 
     save-buffer 

Repeat the following command n 
times 
ESC n 
     digit-argument 

Repeat the following command 4 
times 
C-u 
     universal-argument 

Transpose two letters C-t 
     transpose-chars 

Transpose two words ESC t 
     transpose-words 

Capitalize word ESC c 
     capitalize-word 

Uppercase word ESC u 
     upcase-word 

Enter shell mode ESC x shell 

Start Dired C-x d 
     dired 

Display the day of the year p d 
     calendar-print-day-of-year 

Display diary file s 
     show-all-diary-entries 

Start Gnus ESC x gnus 

Indent each line between the cursor 
and mark 
ESC C-\ 
     indent-region 

Move to the end of current function ESC C-e 
     end-of-defun 

code styles:
cc-mode The default coding style, from which all others are 
derived 
gnu Style used in C code for Emacs itself and other 
GNU-related programs 
k&r Style of the classic text on C, Kernighan and Ritchie's 
The C Programming Language 
bsd Style used in code for BSD-derived versions of UNIX 
stroustrup C++ coding style of the standard reference work, 
Bjarne Stroustrup's The C++ Programming Language 
whitesmith Style used in Whitesmith Ltd.'s documentation for their 
C and C++ compilers 
ellemtel Style used in C++ documentation from Ellemtel 
Telecommunication Systems Laboratories in Sweden 
linux Style used by Linux developers 
python Style used by Python extension developers 
java Style used when writing Java code (entering Java mode 
selects this option by default) 

View the (non-)warranty for Emacs C-h C-w 
     describe-no-warranty