zt, zz and zb are great too. They redraw the screen so that the line the cursor is currently on becomes the top, middle, or bottom line of the window.
:setlocal spell spelllang=en_us - turn on spell check
z= - bring up list of suggestions
zg - add word to dict
zug - undo add to word
zw - mark as wrong
zuw - undo wrong
:help fold
zf<motion> - create fold (common motions '%', 'a{', 'a(' )
zo - open fold
zA - open folds recursively
zc - close fold
zd - forget fold
zj - move to next fold
zk - move to prev fold (up)zR - Open all folds
zM - Close all folds
zO - Open all folds under the cursor recursively
zC - Close all folds under the cursor recursively
zX - Undo manually opened and closed folds: re-apply 'foldlevel'.
zg g = Good word, add to personal dict
zug Undo Good word.
zw obviously, Wrong word.
...
zo Open
zA open All
zc Close
zj uses the same movement as the j key
zk ditto