Unless you have specific types of medical experience, the only/best thing people can do for Haiti is donate funds.
Two extremely well-respected organizations who already have extensive and current experience in Haiti are:
a) Partners In Health and,
b) Red Cross
Note: Any Canadians who make donations to Haiti relief via registered Canadian charities will have their donations matched in full by the Canadian government (via the CIDA-administered Haiti Earthquake Relief Fund) IF they donate prior to February 12th. Other countries may have similar programs in place however I don't have information.