Help is mobilized and en route for the immediate relief effort in Haiti, but as some have pointed out, hurricane season isn't that far away. And when we consider that there are approximately three million people affected by the quake, that translates to a pressing need for workable, rapidly distributable shelter that can hold up to the demands of high winds and heavy rains. Retired shipping containers may be part of the answer.
Interlocking, stackable steel shipping containers are readily available, come in sizes from twenty to forty feet in length, are structurally very sound and even the 'retired' cans are reasonably weathertight. Cutting windows in the sides doesn't seriously affect their structural integrity, which is from the heavy, reinforced edges. They're totally modular, they can be stacked, cantilevered and assembled in multiple configurations and are heavy enough to be stable without being welded, though it's certainly possible to weld them and knock the welds apart and disassemble when real housing can be built.
The idea isn't new, there are already projects getting recognition for innovative and even esthetic uses- 10 Shipping Container Projects of 2009. But as rapidly deployable emergency shelter for an area that needs much more than tents during some parts of the year, they could be ideal.
Port-au-Prince's harbor is currently out of commission, but it can presumably be brought back online in a reasonable amount of time and the containers can always be moved with heavy helicopters, which would be necessary for placement in many areas anyway. Surplus containers are readily available world wide, donations shouldn't be difficult to come by.
Earthships, strawbale construction and other various green building techniques should be seriously considered for permanent rebuilding, (someone mentioned a type of plastic block kit that used existing rubble to fill the construction blocks, more info welcome), but for this year's hurricane season, any of those would take too long to affect a significant percentage of the population, whereas some form of shipping container use is at least plausible.
I think that a significant portion of the city's populace is going to have to spread out into the countryside to reduce the pressure on the overstretched resources of the city for some time. Apparently we're already seeing some migration to find medical assistance and other resources. The pros and cons for encouraging population shifts is a question for city planners and other experts, I don't know what the implications are. But there is time pressure to formulate and implement something that could conceivably safely shelter an enormous number of people in a few months, and shipping containers is the only thing that I can think of that might possibly fit the bill.
Update: Scipio has pointed out that some of these ideas have already been in the works for hurricane rebuilding, courtesy of students at Clemson University
a good link and many thanks for mentioning it.