Aside from New Orleans Mardi Gras, the biggest event in the annual calendar is The New Orleans Jazz and Heritage festival, which takes place at the Fair Grounds Race Course on Gentilly Boulevard, and attracts the big names in Jazz, and many celebrities to the city in late April through until early May.
Other events that may be of interest, and warrant visiting when you are in New Orleans, include the Swamp Festival of Cajun Culture in early October at venues throughout the city, and the voodoo tinged Halloween spectacular, when the streets fill with zombies, and vampires inspired by Anne Rice rather than Dracula.