Basic:
Ctrl + s = search forward
Ctrl + r = search backward
Ctrl + k = cut
Ctrl + y = paste
Ctrl + _ = undo
Ctrl + Space = mark set
Alt + x, [full command] = explore all commands with autocomplete

String replace:
Alt + x, string-replace
Alt + x, query-replace = string replace with Y/N on each matching instance

Files:
Ctrl + x + s = save buffer
Ctrl + x + f = find/open file
Ctrl + x + c = exit
Ctrl + x , b = switch buffer
Ctrl + x , k = kill buffer 

Indenting:
(Ctrl + Alt), \ = indent region

Moving around:
Alt + > = end of buffer
Alt + < = beginning of buffer
Ctrl + p = move up one line
Ctrl + n = move down one line
Ctrl + e = end of line
Ctrl + a = beginning of line

Rectangular Cut:
Ctrl + x, r, k

Macros:
Ctrl + x, ( = begin macro
Ctrl + x, ) = end macro
Ctrl + x, e = execute macro

Interesting:
Ctrl + t = transpose letters
Alt + t = transpose words