some handy key bindings

Emacs offers many handy key bindings; every now and then I come across a new
one, which has been hiding there somewhere for a decade or more… Here are
some of my favorites – I'm listing those that are (a) often useful, (b) might
not be known by everyone already (c) don't require any external packages or
setup.

• 
  M-27 x gives you xxxxxxxxxxxxxxxxxxxxxxxxxxx; and, believe it or not,
  works also with different characters and numbers;
  


• 
  M-m jumps to the first non-whitespace character on the current line;
  


• 
  M-^ joins two lines into one – like vi(m)'s :join,
  except that point must be on the second line, not the first;
  


• 
  M-/ auto-completes based on words in all your buffers; there are more
  powerful alternatives, but this one does not require any setup;
  


• 
  C-h k followed by some key or key combination tells you what it does, C-h m describes the currently active modes, with their key bindings;
  


• 
  C-h f documents the current function, C-h v does the same for
  variables. C-h a gives you information about commands - for example to get
  date-related commands, press C-h a date. This will, however, also get
  you commands related to update; instead, you can use C-h a \bdate
  (because C-h a accepts regular expressions);
  


• 
  C-x C-o will delete all the empty lines around your current cursor
  position, except for one;
  


• 
  M-q re-aligns the current paragraph; I use it all the time when writing
  e-mails etc. (you might want to check out filladapt for a version that gives
  you a bit more smartness with indentations, lists etc.);
  


• 
  C-x 8 RET in a recent emacs version gives you an auto-completable list of
  special characters to insert. So if I need, say, the Yen-character, I type
  C-x 8 RET ye TAB and I get YEN SIGN, which RET will then insert:
  ¥. Note that the completion only works on the start of the character name,
  so if you'd want to include the α-character, you'd need to know that its
  UCS-name is GREEK SMALL LETTER ALPHA… (you can try *alpha or TAB the
  empty string, and search in the results buffer, but that's rather slow);
  


• 
  C-h l shows your last 300 key presses ('lossage'). Interesting to see, and
  it might be useful when defining keyboard macros.
  
  

What are your favorites? Please share them in the comments.