Carnival offers two ships that leave from the Port of Tampa and we have been on both of them! The Inspiration and The Legend both leave and return to Tampa Bay. The Cruise Terminal is right next to the Florida Aquarium, so you could see that on the day you come back also.
They bill themselves as the Fun Ships and it was so fun we went 3 years in a row in September. September has the least expensive prices, but it's also peak Hurricane season, so that's probably why. On our 2007 trip we went a week or two after a major hurricane tore up one of our ports, so that port had to be replaced with another.
Find all of the dates and more information at the Carnival website below.
http://www.carnival.com/Some of our pictures from 2007 are below, so click them to make them larger.