Commands

u - Undo
Ctrl+R - Redo
y - Copy
d - Cut
v - Paste
/\<l\> - Search for single letter (or word) l /pattern - Search for 'pattern'
:set ignorecase - Sets the default search mode to case insensitive
:set number - Displays line numbers
/pattern\c - Search for 'pattern' (case insensitive)
/\cpattern - Search for 'pattern' (case insensitive)
/pat\ctern - Search for 'pattern' (case insensitive)
:%s/search/replace/g - Replace 'search' with 'replace' in the entire file
Ctrl+w, v - Split window vertically
Ctrl+w, s - Split window horizontally
Ctrl+w, w - Switch between split windows
Ctrl+w, q - Quit a window
Shift+g - Go to end of file
gg - Go to beginning of file
Ctrl+v, Tab - Insert a real tab ('\t') character. Useful when you have spaces set instead of tabs.
>> - Indent a line
3>> - Indent a line three times
Shift+v, jj> - Select & indent two lines
>% - Indent a bracketed block (move cursor to starting bracket {)
]p - Paste & indent code
Shift+j - unwrap selected lines

`vim` parameters

vim file1 file2 -o - opens the two files and splits the screen s.t. file1 takes up the top half and file2 takes the bottom half.
vim file1 file2 -O - opens the two files and splits the screen s.t. file1 takes up the left half and file2 takes the right half.

Cut or copy lines without counting

If you ever need to cut/copy/delete/paste lines without knowing the actual number of lines, here is what you should do.

In normal mode, go to the beginning of the section that you want to yank.

Type mk to mark this spot as k.
Go to the end of the section you want to yank using whatever movement commands you like.
Type: y'k (<y-yank>, <single quote-go to mark>, k) To yank from the mark to the current location.
You can paste those lines wherever you want with p

Similarly, d'k will cut/delete the lines from the current location to the mark.

Replace matched group

I wanted to search for 2 leading spaces followed by any uppercase character and insert " * " followed by that upper case character. So I needed to refer to that matched character:

:%s/^  \([A-Z]\)/ * \1/g

The ^ refers to the beginning of a line, the $ and $ are for grouping a match. The [A-Z] matches any single upper case character. The \1 refers to the uppercase character matched in $[A-Z]$.

Replace single letter occurrences

Useful for math symbols:

:%s/\<x\>/m/g

Replaces all occurrences of the single letter x (by itself, not in a word) with the letter m

Search for something with `/` then replace it with `%s`

/keyword
:%s//new_keyword/g

Replace a visually selected yanked block

You have to press y for yanking and then type in :%s/ and then press Ctrl+R and then press " to get the text to show up in in the %s/<here>/ section.

y:%s/<Ctrl+R>"/new text/g

Change each 'foo' to 'bar' for all lines from the current line (.) to the last line ($) inclusive

:.,$s/foo/bar/g

Display whitespace characters (tabs, spaces, newlines, etc.)

:set list

If you want to change the way they are displayed you can use listchars:

:set listchars=eol:$,tab:>-,trail:~,extends:>,precedes:<