ROFLZ!!

Roflmao, rofl, roflz, rofpmsl, roflcopter.

The term "rofl" is simply an internet accronmym for Rolling On Floor Laughing.

Roflmao is the same but some additional information if given, Rolling On Floor Laughing My A$$ Off.

Roflpmsl is simply Rolling On Floor P!$$ing Myself Laughing, mostly it's not literally meant but it's commonly used when something strikes someone as extremely funny.

The term "ROFLCOPTER" originated from the phrase "Roll On Floor Laughing, Can't Operate Properly Till Eyes Refocus". Since then people have adapted this and  Roflcopter games have been created(http://www.rofl.name/f/game_roflcopter), but is still used in the language of the gaming community.