Hurricanes?

Well...your question certainly leaves me with lots of interpretation...what do you mean by "worst"...most deaths? strongest winds? strongest pressure?  just in the United States?

I will leave you with this.  In the modern era (post-1900)...the Galveston Hurricane of 1900 was an incredible human tragedy and was the worst loss of life in the United States.  No satellite data...no modern warning system...and a low lying isolated barrier island was a recipe for disaster.  However...if you want to include total damage from a storm...certainly Katrina ranks very high (note: to fairly compare storms from different years...the storm damage data must be normalized to modern times...for example...the hurricane of 1926 devastated Miami...if the same storm were to hit today...damage might exceed that of Katrina).  However...from an intensity perspective...Hurricane Wilma in the same year that Katrina hit was the most powerful hurricane (based on pressure) ever recorded in the Atlantic basin. 

Finally a little global perspective...Bangladesh...a low lying country in southern Asia...has been devastated repeatedly from tropical cyclones (hurricanes are called tropical cyclones in the Indian Ocean).  In 1970 tropical cyclone Bhola killed over 500,000 people.  Yes...that is the correct number of zeroes.  Even this past hurricane season....in November of 2007...tropical cyclone Sidr killed over 2000 people in Bangladesh.