Map Trim introduced in PyMol 0.99beta11, gives the user the ability to cut out a section of a map and read it back in as a completely new map. This was not previously possible prior to 0.99beta11. (Windows build at PyMol Beta or compile from source).
map_trim map-name, selection-name, buffer
Combined with the convenient new object-name wildcards (!!!), you could for example trim all your maps to 3 Angstroms around ligands with one commmand as follows
map_trim *, organic, 3
With map size now reduced, the map_double command can come in handy to increase mesh density on your figure.