Maemo mapper can calculate most of these itself from your current viewing coordinates.

Copied from another thread:

Turn on auto-download to get a few base maps - so you can find the country / city

To download specific geographical areas, centre the display on, for example, London - stay zoomed out so that the whole area fits into the screen.

Menu -> Maps -> Manage Maps
(There are options for downloading maps by area or along a route)
Select the Zoom tab and choose which zoom-levels you want to download. You probably won't need to go all of the way down to level 1 since at that level you don't get much more benefit, but there'll be a load more maps - I found around level 4 tends to be as far as I usually need to zoom.

Addition: Benson suggested downloading alternate levels, e.g. 3,5,7,9 etc to save space.