Map #16 "Patagonia" 
This map covers Patagonia (Chile and Argentina) from the Golfo San Matías (near the Valdez Peninsula) southward and is of scale 1:3,000,000. On the back is a detailed map of Chiloe.

Later, I discovered others:

Map #17 "Camino Austral - Patagonia Chilena"
At a scale of 1 : 1,100,000, this map covers the area from the Pacific coast to (including) Rta 40 in Argentina, between 41° and 48° latitude, and thus includes Pto Montt, Chiloe, Laguna San Rafael, Coyhaique, Chile Chico, Perito Moreno and Lago Belgrano. On its back is a close-up of the area around Coyhaique. Not bad for someone thinking of pedalling the Carretera Austral, or planning to visit Laguna San Rafael.

Map #18 "Patagonia Sur - Tierra del Fuego"  
This map continues south from Map #17 (but leaves a gap of about 100 km - see below) and extends south to include all of Tierra del Fuego. Thus covered are Lago Viedma, Torres del Paine and Pto Natales, Pto Santa Cruz and Cape Horn. To get the best coverage with the least use of paper, the map does not point exactly north, and the back has a large-scaled map that covers everything from Osorno (north of Pto Montt) all the way to Cape Horn. As an added curiosity, there is a trekking map near Pto Eden, the single stop-over of the ferry from Pto. Natales to Pto. Montt. The loop there is listed as 4-5 days, and makes use of one ferry in the interior, and needs to be accessed via a ferry in the fjords.

Another useful map is the detailed Torres del Paine hiking map, Map #13, which is used by most hikers.

Then, there is a map of the southern Lake District in Chile (Trekking Map "Rutas de Jesuitas", #15 by JLM Mapas), and includes Puerto Montt; the Parque Nacional Alerce Andino; the volcanoes Osorno, Calbuco, Puntiagudo, Tronador, and Puyehue; Bariloche and all Lago Nahuel Huapi (Argentina); Lago Puyehue; and Osorno. It shows the usual geographic detail including contour lines, paved vs unpaved roads, the major hiking trails (the Lonely Planet guide of Patagonia has more) and some enlarged sections. It covers all the area of my loop from Osorno to Bariloche and back to Puerto Montt.

You can order these maps from
http://www.chileaustral.com/shopping/maps.html. I tried it in February 1999 and it worked well. The map was in the mail for 9 days, which is great for mail from Chile. In comparison, mail from the US to Toronto takes five days. Recently (Dec 2000),  Maps 17 and 18 were sent to me by the folks of Chileaustral for evaluation (Many thanks!). They took about 3 weeks to get through the Christmas mail rush and clear Canadian customs.

The company that produces the maps is

JLM Cartografia
Gral. de Canto #105 of.1506
Fono/Fax 236 48 08
Providencia Santiago
Chile

First, familiarize yourself with the various classes of bus transportation. The ones you want have storage underneath the midsection, i.e. the buses between the bigger cities. ( I am not sure that Ushuaia is served by such buses). Next, you have to find the bus terminal that services the route you choose (a town may have several bus terminals): your hotel
or hospedaje staff will know. In Chile, the transportation system is private, i.e. different companies compete and you can shop for best departure times and fares. Go there the day before, check it out, indicate you have a bike to bring along and buy your ticket. There is no charge for the bike, and you will have a fixed seat assigned to you. To get the bike on, they ask you to remove the pedals, possibly wheels, and to turn the handlebar sideways. If you have something to cover the greasy parts of the bike, i.e. a sheet of plastic, they'll appreciate it. In Santiago, the fellow who loaded the bike expected a tip: give it as everybody else does so too, and it might save you some damage from whatever. Such tips were not common in the south: e.g. Puerto Montt and Punto Arenas.
A word of caution: the buses arrive at the "platform" about 15 min's before departure and leave on the button - they don't wait.