1. I laughed so hard at his joke that my stomach ached.
2. I laughed so hard that tears rose to my eyes.
3. I can't remember having such a good laugh in years!
4. It really broke me up.
5. It really made me laugh.
6. He is smiling/grinning from ear to ear.
7. He guffawed.
8. He had us rolling in the aisles.
9. He is laughing a real belly laugh.
10. He burst out laughing.
11. It's hilarious.
12. I couldn't keep from laughing.