1. It's hilarious.
2. I laughed so hard that tears rose to my eyes.
3. I laughed so hard at his joke that my stomach ached.
4. I couldn't keep from laughing.
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.