Maps: Morocco doesn’t have a huge road network, so a single country-wide map with a scale of 1:1,000,000 is sufficient for initial planning and will also show some of the unsurfaced roads suitable for 4WD traffic. With a map of 1:1,000,000 it’s easy to get suckered into days that involve huge distances, so it’s as well to look at an equivalent scale map of your home country to give you an appreciation for what you are planning.
I have most of the maps that are available for Morocco and the two that I favour are the Rough Guide and Michelin 742. These both feature scenic routes shown with a green edging, the Michlin map also indicates with a blue edging those roads that might be closed due to winter snow. Of the two the Rough Guide is best as it’s printed on a plasticised surface that is more resistent to being folded and refolded. Unfortunately it is currently out of print and Rough Guide is being cagey about when—or indeed if—it will be reprinted. So at the moment Michelin 742 is your best bet.
[edit--see Feb 2011 post below]
Guide books: It's always handy to have a general guidebook with you to look up hotels and facilities. I have most of these and the one I tend to carry is Rough Guide. Others include Lonely Planet, Everyman Guides, DK Eyewitness and so forth. For adventure exploration you should get a copy of Chris Scott’s Morocco Overland which focuses mainly on routes in southern Morocco. Stanfords is a great mail order resource for Moroccan maps and guide books.
GPS navigation: The coverage of Morocco included in the Atlantic basemap loaded in Garmin Streetpilot/Quest/Zumo units is actually more detailed and extends further south than the coverage shown in Mapsource. Compare them side-by-side to see. Both TomTom and Garmin now have detailed GPS maps available for Morocco, but unless you are spending considerable time in the country it’s difficult to justify the price.
I use the free-of-charge Marokko Topo GPS maps. I have travelled extensively with these maps and found the roads and tracks are accurate. The most recent version is December 2007. For best results on the road only download the street maps to the GPS unit (i.e. remove the topo overlay from the download to your GPS) as otherwise you can get confused between contour lines and tracks. The Marokko Topo map segments don’t take up much storage space as they don’t include routing information. Consequently, when you come to plan a route using roads, you’ll find the GPS will only use the original basemap roads. Which leads to the second point, that GPS navigation in Morocco is best done as ‘off-road’ straight lines between known waypoints.