* I'm so happy I could burst! (This one plays on the feeling of being so happy you feel like you could explode with joy.)
* Happiness is a warm puppy, but a cold beer is pretty good too. (This one is a bit more lighthearted and combines the feeling of happiness with a fun image.)
* I'm so happy I could eat a horse... but I'd rather have a slice of pie. (This is a humorous twist on the classic phrase, emphasizing the joy of food and happiness.)
* What do you call a happy kangaroo? A jolly jumper! (This one uses the word "jolly" to emphasize happiness and plays on the kangaroo's jumping ability.)
Let me know if you'd like me to come up with some more!