i = insert mode
o = begin insert on new line
R = overwrite mode
ESC = Command mode
: = Last Line Command mode
u = undo the last action to thsi file

Deletion Commands:
x = Delete char under cursor
dd = Delete line
dw = delete to end of word
d<return> = current line and next
d0 = delete to beginning of line
D = delete to end of line
d)/d( = delete to end/beginning of sentance
d}/d{ = delete to end/beginning of paragraph
ndd = delete next n lines
rc = overwrite current char with c 
~ = Change case
. = repeat last command

Navigation:
0/$ = beginning and end of line
1G/G = beginning and end of file
nG = nth line in file
H/M = beginning/middle of screen
CTRL-F/B = Forwards/Backwards one page
w/W = Next word
b/B = Previous word
/<string> = find <string> in file (forwards)
/?<string> = find <string> in file (backwards)

File and I/O Commands:
:w = Save
:wq = Save and quit
ZZ = Save and quit
:q! = Quit w/o saving
:e <file> = Edit another file
:! <Command> = Shell command
:r <file> = insert a file into the current one

Buffers commands:
y_ = yank [_ = usual commands. e.g. 0 = beginning of current line, etc]
Y = yank to end of current line
p = put buffer contents in after current line
p = put buffer contents in before current line
"[a-z]y = yank text into buffer a-z
"[a-z]p = put text from buffer a-z
"[a-z]d = delete text and put into buffer a-z

NB: The last three commands can be qualified as usual.  e.g. y) = to end of sentance.

Misc:
When no text on line, use CTRL-T/D to use auto-indent feature.
:s/foo/bar/igc = generalise query/replace

Automatic Line Wrapping:
:set wraplength=70 (or :set wl=70)
:set wraplength=0 (to turn off)
NB: This doesn't work in vim - use textwidth instead of wraplength

To get a command that wraps the current paragraph ('q' in command mode):
map q !}fmt^M
(use ctrl-V ctrl-M to get ^M)