Cracked me up---
Example: That joke was so funny that it "cracked me up."
Example: That joke was so funny that I almost "died laughing."
Rolling in the aisles---
Example: The comedian was so funny that the audience was "rolling in the aisles."
"Laughed (my/your/his/etc.) head off"---
Example: She thought that his joke was so funny that she "laughed her head off."
"Laughed so loud that (my/your/his/etc.) sides were splitting"---
Example: I laughed so loud that my sides were splitting.