Two layouts: one is a variant of the Grid layout that allows the desired aspect ratio of windows to be specified. The other is like Tall but places a grid with fixed number of rows and columns in the master area and uses an aspect-ratio-specified layout for the slaves.

This module can be used as follows:

 import XMonad.Layout.GridVariants

Then add something like this to your layouts:

 Grid (16/10)

for a 16:10 aspect ratio grid, or

 SplitGrid L 2 3 (2/3) (16/10) (5/100)

for a layout with a 2x3 master grid that uses 2/3 of the screen, and a 16:10 aspect ratio slave grid to its right. The last parameter is again the percentage by which the split between master and slave area changes in response to Expand/Shrink messages.

To be able to change the geometry of the master grid, add something like this to your keybindings:

 ((modm .|. shiftMask, xK_equal), sendMessage $ IncMasterCols 1),
 ((modm .|. shiftMask, xK_minus), sendMessage $ IncMasterCols (-1)),
 ((modm .|. controlMask,  xK_equal), sendMessage $ IncMasterRows 1),
 ((modm .|. controlMask,  xK_minus), sendMessage $ IncMasterRows (-1))