Lets you swap workspace tags, so you can keep related ones next to each other, without having to move individual windows.

Add this import to your xmonad.hs:

import XMonad.Actions.SwapWorkspaces

Then throw something like this in your keys definition:

++
[((modm .|. controlMask, k), windows $ swapWithCurrent i)
    | (i, k) <- zip workspaces [xK_1 ..]]

After installing this update, if you're on workspace 1, hitting mod-ctrl-5 will swap workspaces 1 and 5.

For detailed instructions on editing your key bindings, see the tutorial.