Merriam-Webster's Word of the Day for May 02, 2012 is:

cachinnate • \KAK-uh-nayt\  • verb
: to laugh loudly or immoderately

Examples:
The person sitting beside me at the table cachinnated through the entire dinner party, ruining my enjoyment of the meal.

"'Butler' is so deliciously zany and funny, we cachinnated until our sides hurts." — From a theater review by Christopher Muther in The Boston Globe, March 20, 2004

Did you know?
"Cachinnate" has been whooping it up in English since the 19th century. The word derives from the Latin verb "cachinnare," meaning "to laugh loudly," and "cachinnare" was probably coined in imitation of a loud laugh. As such, "cachinnare" is much like the Old English "ceahhetan," the Old High German "kachazzen," and the Greek "kachazein" — all words of imitative origin that essentially meant "to laugh loudly." Our word "cackle" has a different ancestor than any of these words (the Middle English "cakelen"), but this word, too, is believed to have been modeled after the sound of laughter.